10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

þ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2017

OR

¨ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission file number 1-7584

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

(Exact Name of Registrant as Specified in Its Charter)

Delaware	74-1079400
(State or Other Jurisdiction of Incorporation or Organization)	(I.R.S. Employer Identification No.)
2800 Post Oak Boulevard, Houston, Texas	77056
(Address of Principal Executive Offices)	(Zip Code)

713-215-2000

(Registrant’s Telephone Number, Including Area Code)

Securities registered pursuant to Section 12(b) of the Act:

None

Securities registered pursuant to Section 12(g) of the Act:

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ¨    No  þ

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes  ¨    No  þ

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  þ    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  þ    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    þ

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer ¨	Accelerated filer  ¨	Non-accelerated filer  þ	Smaller reporting company ¨	Emerging growth company ¨
		(Do not check if a smaller reporting company)

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  þ

DOCUMENTS INCORPORATED BY REFERENCE

None

REGISTRANT MEETS THE CONDITIONS SET FORTH IN GENERAL INSTRUCTIONS (I) (1)(a) AND (b) OF FORM 10-K AND IS THEREFORE FILING THIS FORM 10-K WITH THE REDUCED DISCLOSURE FORMAT.

TRANSCONTINTENTAL GAS PIPE LINE COMPANY, LLC

FORM 10-K

TABLE OF CONTENTS

		Page
	PART I
Item 1.	Business	3
Item 1A.	Risk Factors	8
Item 1B.	Unresolved Staff Comments	21
Item 2.	Properties	21
Item 3.	Legal Proceedings	21
Item 4.	Mine Safety Disclosures	21
	PART II
Item 5.	Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities	21
Item 6.	Selected Financial Data (Omitted)	21
Item 7.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	22
Item 7A.	Quantitative and Qualitative Disclosure About Market Risk	27
Item 8.	Financial Statements and Supplementary Data	28
Item 9.	Changes in and Disagreements With Accountants on Accounting and Financial Disclosures	55
Item 9A.	Controls and Procedures	55
Item 9B.	Other Information	56
	PART III
Item 10.	Directors, Executive Officers and Corporate Governance (Omitted)
Item 11.	Executive Compensation (Omitted)
Item 12.	Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters (Omitted)
Item 13.	Certain Relationships and Related Transactions, and Director Independence (Omitted)
Item 14.	Principal Accountant Fees and Services	56
	PART IV
Item 15.	Exhibits and Financial Statement Schedules	57
Item 16.	Form 10-K Summary	59

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DEFINITIONS

We use the following gas measurements in this report:

Bcf – means billion cubic feet.

Mdth – means thousand dekatherms.

Mdth/d – means thousand dekatherms per day.

MMdth – means million dekatherms.

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PART 1

Item 1. Business

In this report, Transcontinental Gas Pipe Line Company, LLC (Transco) is at times referred to in the first person as “we”, “us” or “our”.

Transco is indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which is consolidated by The Williams Companies, Inc. (Williams). In January 2017, Williams permanently waived the WPZ general partner's incentive distribution rights, converted its 2 percent general partner interest in WPZ to a non-economic interest and purchased additional WPZ common units. At December 31, 2017, Williams owns a 74 percent limited partner interest in WPZ.

GENERAL

We are an interstate natural gas transmission company that owns a natural gas pipeline system extending from Texas, Louisiana, Mississippi and the Gulf of Mexico through Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, Pennsylvania and New Jersey to the New York City metropolitan area. We also hold an approximate 45 percent interest in Cardinal Pipeline Company, LLC (Cardinal), an intrastate natural gas pipeline located in North Carolina. Our principal business is the interstate transportation of natural gas which is regulated by the Federal Energy Regulatory Commission (FERC).

At December 31, 2017, our natural gas pipeline, which extends from Texas to New York, had a system-wide delivery capacity totaling approximately 15.0 MMdth of gas per day. During 2017, we completed five fully-contracted expansions, which added more than 2.8 MMdth of firm transportation capacity per day to our pipeline. The system is comprised of approximately 9,700 miles of mainline and branch transmission pipelines, 50 compressor stations, four underground storage fields and one liquefied natural gas (LNG) storage facility. Compression facilities at sea level rated capacity total approximately 2.1 million horsepower.

We have natural gas storage capacity in four underground storage fields located on or near our pipeline system and/or market areas, and we operate two of these storage fields. We also have storage capacity in an LNG storage facility that we own and operate. The total usable gas storage capacity available to us and our customers in such underground storage fields and LNG storage facility and through storage service contracts is approximately 200 Bcf of gas. At December 31, 2017, our customers had stored in our facilities approximately 141 Bcf of gas. In addition, through wholly-owned subsidiaries we operate and own a 35 percent interest in Pine Needle LNG Company, LLC (Pine Needle), an LNG storage facility with 4 Bcf of storage capacity. Storage capacity permits our customers to inject gas into storage during the summer and off-peak periods for delivery during peak winter demand periods.

MARKETS AND TRANSPORTATION

Our natural gas pipeline system serves customers in Texas and 12 southeast and Atlantic seaboard states including major metropolitan areas in Georgia, North Carolina, Washington, D.C., Maryland, New York, New Jersey and Pennsylvania.

Our major customers are public utilities and municipalities that provide service to residential, commercial, industrial and electric generation end users. Shippers on our pipeline system include public utilities, municipalities, intrastate pipelines, direct industrial users, electrical generators, gas marketers and producers. Our three largest customers in 2017 were Duke Energy Corporation, National Grid and The Southern Company, Inc., which accounted for approximately 11.2 percent, 10.0 percent and 9.0 percent, respectively, of our total operating revenues. Our firm transportation agreements are generally long-term agreements with various expiration dates and account for the major portion of our business. Additionally, we offer interruptible transportation services under shorter-term agreements.

Our facilities are divided into eight rate zones. Five are located in the production area and three are located in the market area. Long-haul transportation is gas that is received in one of the production-area zones and delivered in

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a market-area zone. Market-area transportation is gas that is both received and delivered within market-area zones. Production–area transportation is gas that is both received and delivered within production–area zones.

PIPELINE PROJECTS

The pipeline projects listed below were either completed during 2017 or are significant future pipeline projects for which we have customer commitments. In 2018, we expect to invest capital of approximately $1.5 billion in pipeline expansion projects.

Gulf Trace

The Gulf Trace Expansion Project involved an expansion of our existing natural gas transmission system together with greenfield facilities to provide incremental firm transportation capacity from Station 65 in St. Helena Parish, Louisiana westward to a new interconnection with Sabine Pass Liquefaction in Cameron Parish, Louisiana. We placed the project into service on February 1, 2017, and it increased capacity by 1,200 Mdth/d.

Hillabee

The Hillabee Expansion Project involves an expansion of our existing natural gas transmission system from our Station 85 Pooling Point in Choctaw County, Alabama to a new interconnection with the Sabal Trail pipeline in Tallapoosa County, Alabama. The project will be constructed in phases, and all of the project expansion capacity is dedicated to Sabal Trail pursuant to a capacity lease agreement. We placed a portion of Phase I into service on June 14, 2017, and we placed the remainder of Phase I into service on July 11, 2017. Phase I increased capacity by 818 Mdth/d. The in-service date of Phase II is planned for the second quarter of 2020. Together, the first two phases of the project are expected to increase capacity by 1,025 Mdth/d.

In March 2016, WPZ entered into an agreement with the member-sponsors of Sabal Trail to resolve several matters. In accordance with the agreement, the member-sponsors paid WPZ an aggregate amount of $240 million in three equal installments as certain milestones of the project were met. WPZ received the first $80 million payment in March 2016, the second $80 million payment in September 2016 and the third $80 million payment in July 2017. Although the agreement was an obligation between WPZ and the member-sponsors, since the agreement is, in part, related to furthering the completion of the project, we recorded deferred revenue and recognized a non-cash distribution to our parent. This deferred revenue is assigned to our results of operations over the 25-year term of the capacity agreement with Sabal Trail.

In August 2017, the Court of Appeals for the District of Columbia Circuit granted an appeal of the FERC certificate order for the Southeast Market Pipelines projects (which includes a group of related projects, including the Hillabee Expansion Project) filed by certain non-governmental organizations. In doing so, the court (i) remanded the matter to the FERC for preparation of an Environmental Impact Statement (EIS) that conforms with the court's opinion regarding quantifying certain greenhouse gas emissions, and (ii) vacated the FERC's certificate order for the projects, which would be effective following the court's mandate (by court order, the mandate will not issue until after disposition of any timely petitions for rehearing). We, along with other intervenors, and the FERC filed petitions for rehearing with the court to overturn the remedy that would involve vacating the FERC certificate order, but on January 31, 2018, the court denied the petitions. In compliance with the court's directive, on February 5, 2018, the FERC issued a Final Supplemental EIS for the projects, reaffirming that while the projects would result in temporary and permanent impacts on the environment, those impacts would not be significant. On February 6, 2018, we, along with other intervenors, and the FERC filed motions with the court to stay the issuance of the mandate in order to give the FERC time to re-issue the authorizations for the projects. The filing of the motions automatically stays the effectiveness of the court's mandate. If the court's mandate is issued prior to the FERC re-issuing the authorizations for the projects, we believe that the FERC will take the necessary steps (which may include issuing temporary certificate authority) to avoid any lapse in federal authorization for the projects.

Garden State

The Garden State Expansion Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from our Station 210 Pooling Point in New Jersey to a new interconnection on our Trenton Woodbury Lateral in Burlington County, New Jersey. The project will be constructed in two phases. The FERC certificate for the project and the other regulatory approvals necessary to commence

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construction of the project have been received. We placed the initial phase of the project into service on September 9, 2017 and plan to place the remaining portion of the project into service during the first quarter of 2018. The project is expected to increase capacity by 180 Mdth/d.

Dalton

The Dalton Expansion Project involved an expansion of our existing natural gas transmission system together with greenfield facilities to provide incremental firm transportation capacity from our Station 210 Pooling Point in New Jersey to markets in northwest Georgia. On April 1, 2017, we began providing firm transportation service through the mainline portion of the project (from the Station 210 Pooling Point to the interconnection with Gulf South at Holmesville in Mississippi) on an interim basis, and on August 1, 2017, we placed the full project into service. The project increased capacity by 448 Mdth/d.

Atlantic Sunrise

The Atlantic Sunrise Project involves an expansion of our existing natural gas transmission system together with greenfield facilities to provide incremental firm transportation capacity from the northeastern Marcellus producing area to markets along our mainline as far south as our Station 85 Pooling Point in Choctaw County, Alabama. In February 2017, we received approval from the FERC for the project. We placed a portion of the mainline project facilities into service on September 1, 2017, which increased capacity by 400 Mdth/d. We plan to place the full project into service during mid-2018, assuming timely receipt of the remaining regulatory approvals. The full project is expected to increase capacity by 1,700 Mdth/d.

Virginia Southside II

The Virginia Southside II Expansion Project involved an expansion of our existing natural gas transmission system together with greenfield facilities to provide incremental firm transportation capacity from our Station 210 Pooling Point in New Jersey and our Station 165 Pooling Point in Virginia to a proposed delivery point on a new lateral off of our Brunswick Lateral in Virginia. We placed the project into service on December 1, 2017, and it increased capacity by 250 Mdth/d.

New York Bay Expansion

The New York Bay Expansion Project involved an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from Station 195 in Pennsylvania to the Rockaway Delivery Lateral transfer point and the Narrows meter station in New York. We placed the project into service on October 6, 2017, and it increased capacity by 115 Mdth/d.

Gulf Connector

The Gulf Connector Expansion Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from Station 65 in Louisiana to delivery points in Wharton and San Patricio Counties, Texas. In November 2017, we received approval from the FERC for the project. The project will be constructed in two phases, and we plan to place both phases into service during the first half of 2019, assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 475 Mdth/d.

Northeast Supply Enhancement

The Northeast Supply Enhancement Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from Station 195 in Pennsylvania to the Rockaway Delivery Lateral transfer point in New York. We filed an application with the FERC in March 2017 for approval of the project. We plan to place the project into service in late 2019 or during the first half of 2020, assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 400 Mdth/d.

Rivervale South to Market

The Rivervale South to Market Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from the existing Rivervale interconnection with Tennessee Gas Pipeline on our North New Jersey Extension to our existing Central Manhattan meter station in New Jersey and our Station 210 Pooling Point in New Jersey. We filed an application with the FERC in August 2017 for approval of the project. We plan to place the project into service as early as the fourth quarter of 2019, assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 190 Mdth/d.

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Gateway

The Gateway Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from PennEast Pipeline Company's proposed interconnection with our mainline south of Station 205 in New Jersey to our existing Ridgefield meter station in Bergen County, New Jersey and our existing Paterson meter station in Passaic County, New Jersey. We filed an application with the FERC in November 2017 for approval of the project. We plan to place the project into service in the first quarter of 2021, assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 65 Mdth/d.

Southeastern Trail

The Southeastern Trail Project involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from the Pleasant Valley interconnect with Dominion's Cove Point Pipeline in Virginia south to the Station 65 Pooling Point in Louisiana. We expect to file an application with the FERC in the second quarter of 2018 for approval of the project. We plan to place the project into service in late 2020, assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 296 Mdth/d.

RATE MATTERS

FERC regulation requires all terms and conditions of service, including the rates charged, to be filed with and accepted by the FERC before any changes can go into effect. We establish our rates primarily through the FERC's ratemaking process, but we also may negotiate rates with our customers pursuant to the terms of our tariff and FERC policy. Key determinants in the ratemaking process are (1) costs of providing service, including depreciation expense, (2) allowed rate of return, including the equity component of the capital structure and related income taxes, and (3) contract and volume throughput assumptions. The allowed rate of return is determined in each rate case. Rate design and the allocation of costs between the reservation and commodity rates also impact profitability. As a result of these proceedings, certain revenues may be collected subject to refund. We record estimates of rate refund liabilities considering our and third-party regulatory proceedings, advice of counsel and other risks.

Since September 1, 1992, we have designed our rates using the straight fixed-variable (SFV) method of rate design. Under the SFV method of rate design, substantially all fixed costs, including return on equity and income taxes, are included in a reservation charge to customers and all variable costs are recovered through a commodity charge to customers. While the use of SFV rate design limits our opportunity to earn incremental revenues through increased throughput, it also limits our risk associated with fluctuations in throughput.

General rate case (Docket No. RP06-569) On August 31, 2006, we submitted to the FERC a general rate filing principally designed to recover increased costs. The rates became effective March 1, 2007, subject to refund and the outcome of a hearing. All issues in this proceeding except one were resolved by settlement.

The one issue reserved for litigation or further settlement related to our proposal to change the design of the rates for service under our WSS-OA storage rate schedule, which was implemented subject to refund on March 1, 2007. Following a hearing, the FERC issued an opinion approving our proposed incremental rate design, and subsequently denied requests for rehearing of that approval. On February 21, 2014, the U. S. Court of Appeals for the D.C. Circuit (D.C. Circuit) issued an opinion that vacated and remanded the FERC's order because the FERC did not adequately support its conclusions. On March 17, 2016, the FERC issued an order addressing the issues raised by the D.C. Circuit's opinion. In the March 17 order, the FERC reversed its prior opinion and found that Transco's incremental rate design was unjust and unreasonable. The FERC directed Transco to design its WSS-OA rates on a rolled-in basis, to file revised WSS-OA rates reflecting the findings in the order, and to refund the amounts collected in excess of those rates since March 1, 2007. On April 18, 2016, we submitted the compliance filing reflecting rolled-in rates for WSS-OA service consistent with the March 17 order, and began charging those rates beginning April 19, 2016. We also filed a request for rehearing of the March 17 order. On October 4, 2017, the FERC issued an order denying all requests for rehearing of the March 17 order, accepting our April 18, 2016 compliance filing, and directing us to make refunds. No party filed a request for rehearing of the October 4 order, and no party filed an appeal of the March 17, 2016 or October 4, 2017 order. On November 16, 2017, we issued refunds of $19.2 million to the affected customers.

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The rates we charge to our customers are subject to the rate-making policies of the FERC. These policies permit us to include in our cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Cuts and Jobs Act signed into law on December 22, 2017 (Tax Reform), makes significant changes to the U.S. federal income tax rules applicable to both individuals and entities, including among other things, a reduction in corporate federal income tax rates. Although we expect that the decreased federal income tax rates will require us to reduce our rates charged to customers in the future and as a result we recognized a regulatory liability as of the date of enactment of Tax Reform, the details of any regulatory implementation guidance remain uncertain.

REGULATION

FERC Regulation.

Our interstate transmission and storage activities are subject to regulation by the FERC under the Natural Gas Act of 1938, as amended (NGA), and under the Natural Gas Policy Act of 1978, as amended, and as such, our rates and charges for the transportation of natural gas in interstate commerce, the extension, enlargement or abandonment of jurisdictional facilities, and accounting, among other things, are subject to regulation. We hold certificates of public convenience and necessity issued by the FERC authorizing ownership and operation of pipelines, facilities and properties for which certificates are required under the NGA. The FERC’s Standards of Conduct govern the relationship between natural gas transmission providers and marketing function employees as defined by the rule. The standards of conduct are intended to prevent natural gas transmission providers from preferentially benefiting gas marketing functions by requiring the employees of a transmission provider that perform transmission functions to function independently from gas marketing employees and by restricting the information that transmission providers may provide to gas marketing employees. Under the Energy Policy Act of 2005, the FERC is authorized to impose civil penalties of up to $1.2 million per day for each violation of its rules.

Environmental Matters.

Our operations are subject to federal environmental laws and regulations as well as the state and local laws and regulations adopted by the jurisdictions in which we operate. We could incur liability to governments or third parties for any unlawful discharge of pollutants into the air, soil, or water, as well as liability for cleanup costs. Materials could be released into the environment in several ways including, but not limited to:

• Leakage from gathering systems, underground gas storage caverns, pipelines, transportation facilities and storage tanks;

• Damage to facilities resulting from accidents during normal operations;

• Damages to onshore and offshore equipment and facilities resulting from storm events or natural disasters; and

• Blowouts, cratering and explosions.

In addition, we may be liable for environmental damage caused by former owners or operators of our properties.

We believe compliance with current environmental laws and regulations will not have a material adverse effect on our capital expenditures, earnings or current competitive position. However, environmental laws and regulations could affect our business in various ways from time to time, including incurring capital and maintenance expenditures, fines and penalties, and creating the need to seek relief from the FERC for rate increases to recover the costs of certain capital expenditures and operation and maintenance expenses.

For additional information regarding the potential impact of federal, state or local regulatory measures on our business and specific environmental issues, please refer to “Risk Factors – Our operations are subject to environmental laws and regulations, including laws and regulations relating to climate change and greenhouse gas emissions, which may expose us to significant costs, liabilities and expenditures that could exceed our expectations,” and “Environmental Matters” in Note 2 of our Notes to Consolidated Financial Statements.

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Safety and Maintenance.

Our operations are subject to the Natural Gas Pipeline Safety Act of 1968, as amended, the Pipeline Safety Improvement Act of 2002, the Pipeline Safety, Regulatory Certainty, and Jobs Creation Act of 2011 (Pipeline Safety Act), and the Protecting Our Infrastructure of Pipelines and Enhancing Safety Act of 2016 (PIPES Act), which regulate safety requirements in the design, construction, operation and maintenance of interstate natural gas transmission facilities. The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) administers federal pipeline safety laws.

Federal pipeline safety laws authorize PHMSA to establish minimum safety standards for pipeline facilities and persons engaged in the transportation of gas or hazardous liquids by pipeline. These safety standards apply to the design, construction, testing, operation, and maintenance of gas and hazardous liquids pipeline facilities affecting interstate or foreign commerce. PHMSA has also established reporting requirements for operators of gas and hazardous liquid pipeline facilities, as well as provisions for establishing the qualification of pipeline personnel and requirements for managing the integrity of gas transmission and distribution lines and certain hazardous liquid pipelines. To ensure compliance with these provisions, PHMSA performs pipeline safety inspections and has the authority to initiate enforcement actions.

On January 3, 2012, the Pipeline Safety Act was enacted. The Pipeline Safety Act requires PHMSA to complete a number of reports in preparation for potential rulemakings. The issues addressed in these rulemaking provisions include, but are not limited to, the use of automatic or remotely-controlled shut-off valves on new or replaced transmission line facilities, modifying the requirements for pipeline leak detection systems, and expanding the scope of the pipeline integrity management requirements. On June 22, 2016, the PIPES Act was enacted, further strengthening PHMSA's safety authority.

Pipeline Integrity Regulations We have an Integrity Management Plan in compliance with the PHMSA final rule that was issued pursuant to the requirements of the Pipeline Safety Improvement Act of 2002. The rule requires gas pipeline operators to develop an integrity management program for transmission pipelines that could affect high consequence areas in the event of pipeline failure. The Integrity Management Plan includes a baseline assessment plan that was completed in 2012 along with periodic reassessments to be completed within required timeframes. In meeting the integrity regulations, we have identified high consequence areas as defined by the rule. Ongoing periodic reassessments and initial assessments of any new high consequence areas will be completed within the timeframes required by the rule. We estimate that the cost to be incurred in 2018 associated with this program will be approximately $87million. Management considers the costs associated with compliance with the rule to be prudent costs incurred in the ordinary course of business and, therefore, recoverable through our rates.

EMPLOYEES

Transco has no employees. Operations, management and certain administrative services are provided by Williams and its affiliates.

TRANSACTIONS WITH AFFILIATES

We engage in transactions with WPZ, Williams and other Williams’ subsidiaries. (See Note 1 and Note 7 of Notes to Consolidated Financial Statements.)

Item 1A. Risk Factors

FORWARD-LOOKING STATEMENTS

The reports, filings, and other public announcements of Transcontinental Gas Pipe Line Company LLC, may contain or incorporate by reference statements that do not directly or exclusively relate to historical facts. Such statements are “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended (Securities Act), and Section 21E of the Securities Exchange Act of 1934, as amended (Exchange Act). These forward-looking statements relate to anticipated financial performance, management’s plans and objectives for future operations, business prospects, outcome of regulatory proceedings, market conditions and other matters.

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All statements, other than statements of historical facts, included in this report that address activities, events or developments that we expect, believe or anticipate will exist or may occur in the future are forward-looking statements. Forward-looking statements can be identified by various forms of words or phrases such as “anticipates,” “believes,” “seeks,” “could,” “may,” “should,” “continues,” “estimates,” “expects,” “assumes,” “forecasts,” “intends,” “might,” “goals,” “objectives,” “targets,” “planned,” “potential,” “projects,” “scheduled,” “will,” “guidance,” “outlook,” “in-service date” or other similar expressions. These forward-looking statements are based on management’s beliefs and assumptions and on information currently available to management and include, among others, statements regarding:

• Our and our affiliates’ future credit ratings;

• Amounts and nature of future capital expenditures;

• Expansion and growth of our business and operations;

• Expected in-service dates for capital projects;

• Financial condition and liquidity;

• Business strategy;

• Cash flow from operations or results of operations;

• Rate case filings;

• Natural gas prices, supply, and demand; and

• Demand for our services.

Forward-looking statements are based on numerous assumptions, uncertainties, and risks that could cause future events or results to be materially different from those stated or implied in this report. Many of the factors that will determine these results are beyond our ability to control or predict. Specific factors that could cause actual results to differ from results contemplated by forward-looking statements include, among others, the following:

• Availability of supplies, including lower than anticipated volumes from third parties and market demand;

• Volatility of pricing including the effect of lower than anticipated energy commodity prices and margins;

• Inflation, interest rates, and general economic conditions (including future disruptions and volatility in the global credit markets and the impact of these events on our customers and suppliers);

• The strength and financial resources of our competitors and the effects of competition;

• Whether we are able to successfully identify, evaluate and timely execute our capital projects and other investment opportunities in accordance with our capital expenditure budget;

• Our ability to successfully expand our facilities and operations;

• Development and rate of adoption of alternative energy sources;

• Availability of adequate insurance coverage and the impact of operational and development hazards and unforeseen interruptions;

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• The impact of existing and future laws (including, but not limited to, the Tax Cuts and Jobs Act of 2017), regulations, the regulatory environment, environmental liabilities, and litigation, as well as our ability to obtain necessary permits and approvals and achieve favorable rate proceeding outcomes;

• Our costs for defined benefit pension plans and other postretirement benefit plans sponsored by our affiliates;

• Changes in maintenance and construction costs;

• Changes in the current geopolitical situation;

• Our exposure to the credit risks of our customers and counterparties;

• Risks related to financing, including restrictions stemming from our debt agreements, future changes in our credit ratings and the availability and cost of capital;

• Risks associated with weather and natural phenomena, including climate conditions and physical damage to our facilities;

• Acts of terrorism, including cybersecurity threats, and related disruptions; and

• Additional risks described in our filings with the Securities and Exchange Commission (SEC).

Given the uncertainties and risk factors that could cause our actual results to differ materially from those contained in any forward-looking statement, we caution investors not to unduly rely on our forward-looking statements. We disclaim any obligations to and do not intend to update the above list or to announce publicly any revisions to any of the forward-looking statements to reflect future events or developments.

In addition to causing our actual results to differ, the factors listed above and referred to below may cause our intentions to change from those statements of intention set forth in this report. Such changes in our intentions may also cause our results to differ. We may change our intentions, at any time and without notice, based upon changes in such factors, our assumptions, or otherwise.

Because forward-looking statements involve risks and uncertainties, we caution that there are important factors, in addition to those listed above, that may cause actual results to differ materially from those contained in the forward-looking statements. These factors are described in the following section.

RISK FACTORS

You should carefully consider the following risk factors in addition to the other information in this report. If any of the risks discussed below occur, our business, prospects, financial condition, results of operations, cash flows and, in some cases our reputation, could be materially adversely affected. Each of these factors could adversely affect our business, operating results, and financial condition as well as adversely affect the value of an investment in our securities.

Risks Inherent to Our Industry and Business

Our natural gas transportation and storage activities involve numerous risks and hazards that might result in accidents and unforeseen interruptions.

Our operations are subject to all the risks and hazards typically associated with the transportation and storage of natural gas including, but not limited to:

• Aging infrastructure and mechanical problems;

• Damages to pipelines and pipeline blockages or other pipeline interruptions;

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• Uncontrolled releases of natural gas;

• Operator error;

• Damage caused by third party activity, such as operation of construction equipment;

• Pollution and other environmental risks; and

• Fires, blowouts, cratering and explosions.

Any of these risks could result in loss of human life, personal injuries, significant damage to property, environmental pollution, impairment of our operations, loss of services to our customers, reputational damage and substantial losses to us. The location of certain segments of our pipeline in or near populated areas, including residential areas, commercial business centers and industrial sites, could increase the level of damages resulting from these risks. An event such as those described above could cause considerable harm and have a material adverse effect on our financial condition and results of operations, particularly if the event is not fully covered by insurance.

Certain of our services are subject to long-term, fixed-price contracts that are not subject to adjustment, even if our cost to perform such services exceeds the revenues received from such contracts.

We provide some services pursuant to long-term, fixed-price contracts. It is possible that costs to perform services under such contracts will exceed the revenues we collect for our services. Although most of the services are priced at cost-based rates that are subject to adjustment in rate cases, under the FERC policy, a regulated service provider and a customer may mutually agree to sign a contract for service at a “negotiated rate” that may be above or below the FERC regulated cost-based rate for that service. These “negotiated rate” contracts are not generally subject to adjustment for increased costs that could be produced by inflation or other factors relating to the specific facilities being used to perform the services.

We may not be able to extend or replace expiring natural gas transportation and storage contracts at favorable rates, on a long-term basis or at all.

Our primary exposure to market risk occurs at the time the terms of existing transportation and storage contracts expire or are subject to termination. Upon expiration or termination of our existing contracts, we may not be able to extend such contracts with existing customers or obtain replacement contracts at favorable rates, on a long-term basis or at all. Failure to extend or replace a significant portion of our existing contracts may have a material adverse effect on our business, financial condition, results of operations and cash flows. Our ability to extend or replace existing customer contracts on favorable terms is subject to a number of factors, some of which are beyond our control, including:

• The level of existing and new competition to deliver natural gas to our markets and competition from alternative fuel sources such as electricity, coal, fuel oils, or nuclear energy;

• Pricing, demand, availability and margins for natural gas in our markets;

• Whether the market will continue to support long-term firm contracts;

• The effects of regulation on us, our customers and our contracting practices; and

• The ability to understand our customers’ expectations, efficiently and reliably deliver high quality services and effectively manage customer relationships. The results of these efforts will impact our reputation and positioning in the market.

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Competitive pressures could lead to decreases in the volume of natural gas contracted for or transported through our pipeline system.

The principal elements of competition among natural gas transportation and storage assets are rates, terms of service, access to natural gas supplies, flexibility, and reliability. Although most of our pipeline system’s current capacity is fully contracted, the FERC has taken certain actions to strengthen market forces in the interstate natural gas pipeline industry that have led to increased competition throughout the industry. Similarly, a highly liquid competitive commodity market in natural gas and increasingly competitive markets for natural gas services, including competitive secondary markets in pipeline capacity, have developed. As a result, pipeline capacity is being used more efficiently, and peaking and storage services are increasingly effective substitutes for annual pipeline capacity. As a result, we could experience some “turnback” of firm capacity as the primary terms of existing agreements expire. If we are unable to remarket this capacity or can remarket it only at substantially discounted rates compared to previous contracts, we or our remaining customers may have to bear the costs associated with the turned back capacity.

We compete primarily with other interstate pipelines and storage facilities in the transportation and storage of natural gas. Some of our competitors may have greater financial resources and access to greater supplies of natural gas than we do. Some of these competitors may expand or construct transportation and storage systems that would create additional competition for natural gas supplies or the services we provide to our customers. Moreover, WPZ and its other affiliates, including Williams, may not be limited in their ability to compete with us. In a number of key markets, interstate pipelines are now facing competitive pressure from other major pipeline systems, enabling local distribution companies and end users to choose a transmission provider based on considerations other than location. Other entities could construct new pipelines or expand existing pipelines that could potentially serve the same markets as our pipeline system. Any such new pipelines could offer transportation services that are more desirable to shippers because of locations, facilities, or other factors. These new pipelines could charge rates or provide service to locations that would result in greater net profit for shippers and producers and thereby force us to lower the rates charged for service on our pipeline in order to extend our existing transportation service agreements or to attract new customers. We are aware of proposals by competitors to expand pipeline capacity in certain markets we also serve which, if the proposed projects proceed, could increase the competitive pressure upon us. Further, natural gas also competes with other forms of energy available to our customers, including electricity, coal, fuel oils, and other alternative energy sources. We may not be able to successfully compete against current and future competitors and any failure to do so could have a material adverse effect on our business, financial condition, results of operations,and cash flows.

Any significant decrease in supplies of natural gas in the supply basins we access or in demand for those supplies in the markets we serve could adversely affect our business and operating results.

Our ability to maintain and expand our business depends on the level of drilling and production by third parties in our supply basins. Production from existing wells and natural gas supply basins with access to our pipeline will naturally decline over time. The amount of natural gas reserves underlying these existing wells may also be less than anticipated, and the rate at which production from these reserves declines may be greater than anticipated. We do not obtain independent evaluations of natural gas reserves underlying such wells and supply basins with access to our pipeline. Accordingly, we do not have independent estimates of total reserves dedicated to our pipeline or the anticipated life of such reserves. In addition, low prices for natural gas, regulatory limitations, including environmental regulations, or the lack of available capital for these projects could adversely affect the development and production of additional reserves, as well as gathering, storage, pipeline transportation, and import and export of natural gas supplies. Localized low natural gas prices in one or more of our existing supply basins, whether caused by a lack of infrastructure or otherwise, could also result in depressed natural gas production in such basins and limit the supply of natural gas made available to us. The competition for natural gas supplies to serve other markets could also reduce the amount of natural gas supply for our customers.

Demand for our transportation services depends on the ability and willingness of shippers with access to our facilities to satisfy demand in the markets we serve by deliveries through our system. Any decrease in this demand could adversely affect our business. Demand for natural gas is also affected by weather, future industrial and economic conditions, fuel conservation measures, alternative fuel requirements, governmental regulation, and technological advances in fuel economy and energy generation devices, all of which are matters beyond our control.

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A failure to obtain sufficient natural gas supplies or a reduction in demand for our services in the markets we serve could have a material adverse effect on our business, financial condition, results of operations and cash flows.

Significant prolonged changes in natural gas prices could affect supply and demand and cause a reduction in or termination of our long-term transportation and storage contracts or throughput on our system.

Higher natural gas prices over the long term could result in a decline in the demand for natural gas and, therefore, in our long-term transportation and storage contracts or throughput on our system. Also, lower natural gas prices over the long term could result in a decline in the production of natural gas resulting in reduced contracts or throughput on our system. As a result, significant prolonged changes in natural gas prices could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Our costs of testing, maintaining or repairing our facilities may exceed our expectations, and the FERC may not allow, or competition in our markets may prevent our recovery of such costs in the rates we charge for our services.

We have experienced and could experience in the future unexpected leaks or ruptures on our gas pipeline system. Either as a preventative measure or in response to a leak or another issue, we could be required by regulatory authorities to test or undertake modifications to our systems. If the cost of testing, maintaining, or repairing our facilities exceed expectations and the FERC does not allow us to recover, or competition in our markets prevents us from recovering such costs in the rates that we charge for our services, such costs could have a material adverse impact on our business, financial condition, results of operations, and cash flows.

The operation of our businesses might be adversely affected by regulatory proceedings, changes in government regulations or in their interpretation or implementation, or the introduction of new laws or regulations applicable to our businesses or our customers.

Public and regulatory scrutiny of the energy industry has resulted in the proposal and/or implementation of increased regulations. Such scrutiny has also resulted in various inquiries, investigations, and court proceedings, including litigation of energy industry matters. Both the shippers on our pipeline and regulators have rights to challenge the rates we charge under certain circumstances. Any successful challenge could materially affect our results of operations.

Certain inquiries, investigations, and court proceedings are ongoing. Adverse effects may continue as a result of the uncertainty of these ongoing inquiries, investigations, and court proceedings, or additional inquiries and proceedings by federal or state regulatory agencies or private plaintiffs. In addition, we cannot predict the outcome of any of these inquiries or whether these inquiries will lead to additional legal proceedings against us, civil or criminal fines and/or penalties, or other regulatory action, including legislation, which might be materially adverse to the operation of our business and our revenues and net income or increase our operating costs in other ways. Current legal proceedings or other matters including environmental matters, suits, regulatory appeals and similar matters might result in adverse decisions against us, which among other outcomes, could result in the imposition of substantial penalties and fines and could damage our reputation. The result of such adverse decisions, either individually or in the aggregate, could be material and may not be covered fully or at all by insurance.

In addition, existing regulations, including those pertaining to financial assurances to be provided by our businesses in respect of potential asset decommissioning and abandonment activities, might be revised, reinterpreted or otherwise enforced in a manner which differs from prior regulatory action. New laws and regulations might also be adopted or become applicable to us, our customers or our business activities. If new laws or regulations are imposed relating to oil and gas extraction, or if additional or revised levels of reporting, regulation, or permitting moratoria are required or imposed, including those related to hydraulic fracturing, the volumes of natural gas that we transport could decline, our compliance costs could increase and our results of operations could be adversely affected.

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Our operations are subject to environmental laws and regulations, including laws and regulations relating to climate change and greenhouse gas emissions, which may expose us to significant costs, liabilities and expenditures that could exceed our expectations.

Our operations are subject to extensive federal, state and local laws and regulations governing environmental protection, endangered and threatened species, the discharge of materials into the environment, and the security of chemical and industrial facilities. Substantial costs, liabilities, delays, and other significant issues related to environmental laws and regulations are inherent in the gathering, transportation, and storage of natural gas as well as waste disposal practices and construction activities. New or amended environmental laws and regulations can also result in significant increases in capital costs we incur to comply with such laws and regulations.

Failure to comply with laws, regulations and permits may result in the assessment of administrative, civil and/or criminal penalties, the imposition of remedial obligations, the imposition of stricter conditions on or revocation of permits, the issuance of injunctions limiting or preventing some or all of our operations and delays or denials in granting permits.

Joint and several, strict liability may be incurred without regard to fault under certain environmental laws and regulations for the remediation of contaminated areas and in connection with spills or releases of materials associated with natural gas, oil, and wastes on, under, or from our properties and facilities. Private parties, including the owners of properties through which our pipeline system passes and facilities where our wastes are taken for reclamation or disposal, may have the right to pursue legal actions to enforce compliance as well as to seek damages for noncompliance with environmental laws and regulations or for personal injury or property damage arising from our operations. Some sites at which we operate are located near current or former third party hydrocarbon storage and processing or oil and natural gas operations or facilities, and there is a risk that contamination has migrated from those sites to ours.

We are generally responsible for all liabilities associated with the environmental condition of our facilities and assets, whether acquired or developed, regardless of when the liabilities arose and whether they are known or unknown. In connection with certain acquisitions and divestitures, we could acquire, or be required to provide indemnification against, environmental liabilities that could expose us to material losses, which may not be covered by insurance. In addition, the steps we could be required to take to bring certain facilities into compliance could be prohibitively expensive, and we might be required to shut down, divest or alter the operation of those facilities, which might cause us to incur losses.

In addition, climate change and the costs that may be associated with its impacts and with the regulation of emissions of greenhouse gases (GHG) have the potential to affect our business. Regulatory actions by the U.S. Environmental Protection Agency (EPA) or the passage of new climate change laws or regulations could result in increased costs to operate and maintain our facilities, install new emissions controls on our facilities, or administer and manage any GHG emissions program. If we are unable to recover or pass through a significant level of our costs related to complying with climate change regulatory requirements imposed on us, it could have a material adverse effect on our results of operations and financial condition. To the extent financial markets view climate change and GHG emissions as a financial risk, this could negatively impact our cost of and access to capital. Climate change and GHG regulation could also reduce demand for our services.    

We depend on certain key customers for a significant portion of our revenues. The loss of any of these key customers or the loss of any contracted volumes could result in a decline in our business.

We rely on a limited number of customers for a significant portion of our revenues. Although some of these customers are subject to long-term contracts, we may be unable to negotiate extensions or replacements of these contracts on favorable terms, or at all. For the year ended December 31, 2017, our largest customer was Duke Energy Corporation, which accounted for approximately 11.2 percent of our operating revenues. The loss of all, or even a portion of, the revenues from contracted volumes supplied by our key customers, as a result of competition, creditworthiness, inability to negotiate extensions or replacements of contracts, or otherwise, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

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We are exposed to the credit risk of our customers and counterparties and our credit risk management will not be able to completely eliminate such risk.

We are subject to the risk of loss resulting from nonpayment and/or nonperformance by our customers and counterparties in the ordinary course of our business. Generally, our customers are rated investment grade, are otherwise considered creditworthy, or are required to make pre-payments or provide security to satisfy credit concerns. However, our credit procedures and policies cannot completely eliminate customer credit risk. Our customers and counterparties include industrial customers, local distribution companies, natural gas producers, and marketers whose creditworthiness may be suddenly and disparately impacted by, among other factors, commodity price volatility, deteriorating energy market conditions, and public and regulatory opposition to energy producing activities. In a low commodity price environment certain of our customers could be negatively impacted causing them significant economic stress including, in some cases, to file for bankruptcy protection or to renegotiate contracts. To the extent one or more of our key customers commences bankruptcy proceedings, our contracts with the customers may be subject to rejection under applicable provisions of the United States Bankruptcy Code, or may be renegotiated. Further, during any such bankruptcy proceeding, prior to assumption, rejection or renegotiation of such contracts, the bankruptcy court may temporarily authorize the payment of value for our services less than contractually required, which could have a material adverse effect on our business, results of operations, cash flows and financial condition. If we fail to adequately assess the creditworthiness of existing or future customers and counterparties, or otherwise do not take sufficient mitigating actions, including obtaining sufficient collateral, deterioration in their creditworthiness and any resulting increase in nonpayment and/or nonperformance by them could cause us to write down or write off accounts receivable. Such write-downs or write-offs could negatively affect our operating results for the period in which they occur, and, if significant, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

If third-party pipelines and other facilities interconnected to our pipeline and facilities become unavailable to transport natural gas, our revenues could be adversely affected.

We depend upon third-party pipelines and other facilities that provide delivery options to and from our pipeline and storage facilities for the benefit of our customers. Because we do not own these third-party pipelines or facilities, their continuing operation is not within our control. If these pipelines or other facilities were to become temporarily or permanently unavailable for any reason, or if throughput were reduced because of testing, line repair, damage to pipelines or facilities, reduced operating pressures, lack of capacity, increased credit requirements or rates charged by such pipelines or facilities or other causes, we and our customers would have reduced capacity to transport, store or deliver natural gas to end use markets, thereby reducing our revenues. Any temporary or permanent interruption at any key pipeline interconnection causing a material reduction in volumes transported on our pipeline or stored at our facilities could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We do not own all of the land on which our pipeline and facilities are located, which could disrupt our operations.

We do not own all of the land on which our pipeline and facilities have been constructed. As such, we are subject to the possibility of increased costs to retain necessary land use. In those instances in which we do not own the land on which our facilities are located, we obtain the rights to construct and operate our pipeline on land owned by third parties and governmental agencies for a specific period of time. Our loss of any of these rights, through our inability to renew right-of-way contracts or otherwise, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We do not insure against all potential risks and losses and could be seriously harmed by unexpected liabilities or by the inability of our insurers to satisfy our claims.

In accordance with customary industry practice, we maintain insurance against some, but not all, risks and losses, and only at levels we believe to be appropriate. The occurrence of any risks not fully covered by insurance could have a material adverse effect on our business, financial condition, results of operations, and cash flows, and our ability to repay our debt.

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We may not be able to grow or effectively manage our growth.

As part of our growth strategy, we engage in significant capital projects. We have a project lifecycle process and an investment evaluation process. These are processes we use to identify, evaluate, and execute on acquisition opportunities and capital projects. We may not always have sufficient and accurate information to identify and value potential opportunities and risks or our investment evaluation process may be incomplete or flawed. Our growth may also be dependent upon the construction of new natural gas gathering, transportation, compression, processing, or treating pipelines and facilities, as well as the expansion of existing facilities. In the current environment, we may face political opposition by landowners, environmental activists and others resulting in the delay and/or denial of required governmental permits. Additional risks associated with construction may include the inability to obtain rights-of-way, skilled labor, equipment, materials, permits and other required inputs in a timely manner such that projects are completed on time and the risk that construction cost overruns could cause total project costs to exceed budgeted costs. Additional risks associated with growing our business include, among others, that:

• Changing circumstances and deviations in variables could negatively impact our investment analysis, including our projections of revenues, earnings, and cash flow relating to potential investment targets, resulting in outcomes which are materially different than anticipated;

• We could be required to contribute additional capital to support acquired businesses or assets. We may assume liabilities that were not disclosed to us that exceed our estimates and for which contractual protections are either unavailable or prove inadequate;

• Acquisitions could disrupt our ongoing business, distract management, divert financial and operational resources from existing operations and make it difficult to maintain our current business standards, controls, and procedures; and

• Acquisitions and capital projects may require substantial new capital, including the issuance of debt or equity, and we may not be able to access credit or capital markets or obtain acceptable terms.

If realized, any of these risks could have an adverse impact on our financial condition, results of operations, including the possible impairment of our assets, or cash flows.

Risks Related to Strategy and Financing

A downgrade of our credit ratings, which are determined outside of our control by independent third parties, could impact our liquidity, access to capital and our costs of doing business.

Downgrades of our credit ratings increase our cost of borrowing and could require us to provide collateral to our counterparties, negatively impacting our available liquidity. In addition, our ability to access capital markets could be limited by a downgrade of our credit ratings. Credit rating agencies perform independent analysis when assigning credit ratings. The analysis includes a number of criteria such as business composition, market and operational risks, as well as various financial tests. Credit rating agencies continue to review the criteria for industry sectors and various debt ratings and may make changes to those criteria from time to time. Credit ratings are subject to revision or withdrawal at any time by the credit ratings agencies.

Our ability to obtain credit in the future could be affected by Williams’ and WPZ’s credit ratings.

Substantially all of Williams’ and WPZ’s operations are conducted through their respective subsidiaries. Each of Williams’ and WPZ’s cash flows are substantially derived from loans, dividends and distributions paid to them by their subsidiaries. Due to our relationship with each of Williams and WPZ, our ability to obtain credit will be affected by Williams’ and WPZ’s credit ratings. If Williams or WPZ were to experience a deterioration in its respective credit standing or financial condition, our access to capital and our ratings could be adversely affected. Any downgrading of a Williams or WPZ credit rating could result in a downgrading of our credit rating. A downgrading of a Williams or WPZ credit rating could limit our ability to obtain financing in the future upon favorable terms, if at all.

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Restrictions in our debt agreements and the amount of our indebtedness may affect our future financial and operating flexibility.

Our total outstanding long-term debt (including current portion) as of December 31, 2017, was $2.44 billion.

The agreements governing our indebtedness contain covenants that restrict our ability to incur certain liens to support indebtedness and our ability to merge or consolidate or sell all or substantially all of our assets. In addition, certain of our debt agreements contain various covenants that restrict or limit, among other things, our ability to guarantee certain indebtedness, to make certain distributions during the continuation of an event of default and to enter into certain affiliate transactions and certain restrictive agreements and to change the nature of our business. Certain of our debt agreements also contain, and those we enter into in the future may contain, financial covenants and other limitations with which we will need to comply. Williams’ and WPZ’s debt agreements contain similar covenants with respect to such entities and their respective subsidiaries, including us.

Our debt service obligations and the covenants described above could have important consequences. For example, they could, among other things:

• Make it more difficult for us to satisfy our obligations with respect to our indebtedness, which could in turn result in an event of default on such indebtedness;

• Impair our ability to obtain additional financing in the future for working capital, capital expenditures, general limited liability company purposes, or other purposes;

• Diminish our ability to withstand a continued or future downturn in our business or the economy generally;

• Require us to dedicate a substantial portion of our cash flow from operations to debt service payments, thereby reducing the availability of cash for working capital, capital expenditures, general limited liability company purposes, or other purposes; and

• Limit our flexibility in planning for, or reacting to, changes in our business and the industry in which we operate, including by limiting our ability to expand or pursue our business activities and by preventing us from engaging in certain transactions that might otherwise be considered beneficial to us.

Our ability to comply with our debt covenants, to repay, extend or refinance our existing debt obligations and to obtain future credit will depend primarily on our operating performance. Our ability to refinance existing debt obligations or obtain future credit will also depend upon the current conditions in the credit markets and the availability of credit generally. If we are unable to comply with these covenants, meet our debt service obligations, or obtain future credit on favorable terms, or at all, we could be forced to restructure or refinance our indebtedness, seek additional equity capital, or sell assets. We may be unable to obtain financing or sell assets on satisfactory terms, or at all.

Our failure to comply with the covenants in the documents governing our indebtedness could result in events of default, which could render such indebtedness due and payable. We may not have sufficient liquidity to repay our indebtedness in such circumstances. In addition, cross-default or cross-acceleration provisions in our debt agreements could cause a default or acceleration to have a wider impact on our liquidity than might otherwise arise from a default or acceleration of a single debt instrument. For more information regarding our debt agreements, please read “Management’s Discussion and Analysis of Financial Condition and Results of Operations - Capital Resources and Liquidity”.

Difficult conditions in the global financial markets and the economy in general could negatively affect our business and results of operations.

Our business may be negatively impacted by adverse economic conditions or future disruptions in the global financial markets. Included among these potential negative impacts are industrial or economic contraction leading to reduced energy demand and lower prices for our products and services and increased difficulty in collecting amounts owed to us by our customers. We have availability under the credit facility, but our ability to borrow under that facility

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could be impaired if one or more of our lenders fails to honor its contractual obligation to lend to us. If financing is not available when needed, or is available only on unfavorable terms, we may be unable to implement our business plans or otherwise take advantage of business opportunities or respond to competitive pressures. In addition, financial markets have periodically been affected by concerns over U.S. fiscal and monetary policies. These concerns, as well as actions taken by the U.S. federal government in response to these concerns, could significantly and adversely impact the global and U.S. economies and financial markets, which could negatively impact us in the manner described above.

WPZ can exercise substantial control over our distribution policy and our business and operations and may do so in a manner that is adverse to our interests.

Because we are an indirect wholly-owned subsidiary of WPZ, WPZ exercises substantial control over our business and operations and makes determinations with respect to, among other things, the following:

• Payment of distributions and repayment of advances;

• Decisions on financings and our capital raising activities;

• Mergers or other business combinations; and

• Acquisition or disposition of assets.

WPZ could decide to increase distributions or advances to our member consistent with existing debt covenants. This could adversely affect our liquidity.

Risks Related to Regulations That Affect Our Industry

Our natural gas transportation and storage operations are subject to regulation by the FERC, which could have an adverse impact on our ability to establish transportation and storage rates that would allow us to recover the full cost of operating our pipeline, including a reasonable rate of return.

In addition to regulation by other federal, state, and local regulatory authorities, under the NGA, our interstate pipeline transportation and storage services and related assets are subject to regulation by the FERC. Federal regulation extends to such matters as:

• Transportation of natural gas in interstate commerce;

• Rates, operating terms, types of services and conditions of service;

• Certification and construction of new interstate pipeline and storage facilities;

• Acquisition, extension, disposition, or abandonment of existing interstate pipelines and storage facilities;

• Accounts and records;

• Depreciation and amortization policies;

• Relationships with affiliated companies who are involved in marketing functions of the natural gas business; and

• Market manipulation in connection with interstate sales, purchases, or transportation of natural gas.

Regulatory or administrative actions in these areas, including successful complaints or protests against our rates, can affect our business in many ways, including by decreasing existing tariff rates or setting future tariff rates to levels such that revenues are inadequate to recover increases in operating costs or to sustain an adequate return on capital

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investments, decreasing volumes in our pipelines, increasing our costs and otherwise altering the profitability of our business.

Unlike other interstate pipelines that own facilities in the offshore Gulf of Mexico, we charge our transportation customers a separate fee to access our offshore facilities. The separate charge is referred to as an “IT feeder” charge. The “IT feeder” rate is charged only when gas is actually transported on the facilities and typically it is paid by producers or marketers. Because the “IT feeder” rate is typically paid by producers and marketers, it generally results in netback prices to producers that are slightly lower than the netbacks realized by producers transporting on other interstate pipelines. This rate design disparity can result in producers bypassing our offshore facilities in favor of alternative transportation facilities.

The amount of income taxes that we will be allowed to recover will be determined by the outcome of future rate cases and any potential action taken by the FERC in response to its recent Notice of Inquiry.

In May 2005, the FERC issued a statement of general policy permitting a pipeline to include in its cost-of-service computations an income tax allowance provided that an entity or individual has an actual or potential income tax liability on income from the pipeline’s public utility assets. Pursuant to that policy, the extent to which owners of pipelines have such actual or potential income tax liability will be reviewed by the FERC on a case-by-case basis in rate cases where the amounts of the allowances will be established. In December 2016, the FERC issued a Notice of Inquiry (NOI) in response to the holding of the U.S. Court of Appeals for the District of Columbia Circuit in United Airlines, Inc., et al. v. Federal Energy Regulatory Commission that the FERC failed to demonstrate that there is no double recovery of taxes for a partnership pipeline as a result of the income tax allowance and return on equity determined pursuant to the discounted cash flow methodology. Accordingly, the Court remanded the decision to the FERC to develop a mechanism “for which the FERC can demonstrate that there is no double recovery” of partnership income tax costs. The FERC’s NOI seeks further information from the pipeline industry as the FERC re-evaluates its policies following the United Airlines decision.

We expect that certain aspects of Tax Reform, including regulatory liabilities relating to reduced corporate federal income tax rates, could adversely impact our financial condition and our future financial results.

Certain of the rates we charge to our customers are subject to the rate-making policies of the FERC. These policies permit us to include in our cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Reform makes significant changes to the U.S. federal income tax rules applicable to both individuals and entities, including among other things, a reduction in corporate federal income tax rates. Although we expect the decreased federal income tax rates will require us to return amounts to certain customers for this item through future rates and have recognized a regulatory liability, the details of any regulatory implementation guidance remain uncertain.

Risks Related to Employees and Outsourcing of Support Activities

Failure of our service providers or disruptions to outsourcing relationships might negatively impact our ability to conduct our business.

We rely on Williams and other third parties for certain services necessary for us to be able to conduct our business. We have a limited ability to control these operations and the associated costs. Certain of the Williams’ accounting and information technology functions that we rely on are currently provided by third party vendors, and sometimes from service centers outside of the United States. Services provided pursuant to these agreements could be disrupted. Similarly, the expiration of such agreements or the transition of services between providers could lead to loss of institutional knowledge or service disruptions. Our reliance on Williams and others as service providers and on Williams’ outsourcing relationships, and our limited ability to control certain costs, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

A failure to attract and retain an appropriately qualified workforce could negatively impact our results of operations.

Events such as an aging workforce without appropriate replacements, mismatch of skill sets to future needs, or unavailability of contract labor may lead to operating challenges such as lack of resources, loss of knowledge, and a

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lengthy time period associated with skill development, including with the workforce needs associated with projects and ongoing operations. Williams’ failure to hire and adequately obtain replacement employees, including the ability to transfer significant internal historical knowledge and expertise to the new employees, or the future availability and cost of contract labor may adversely affect our ability to manage and operate the businesses. If Williams is unable to successfully attract and retain an appropriately qualified workforce, results of operations could be negatively impacted.

Our allocation from Williams for costs for its defined benefit pension plans and other postretirement benefit plans are affected by factors beyond our and Williams’ control.

As we have no employees, employees of Williams and its affiliates provide services to us. As a result, we are allocated a portion of Williams’ costs in defined benefit pension plans covering substantially all of Williams’ or its affiliates’ employees providing services to us, as well as a portion of the costs of other postretirement benefit plans covering certain eligible participants providing services to us. The timing and amount of our allocations under the defined benefit pension plans depend upon a number of factors that Williams controls, including changes to pension plan benefits, as well as factors outside of Williams’ control, such as asset returns, interest rates and changes in pension laws. Changes to these and other factors that can significantly increase our allocations could have a significant adverse effect on our results of operations and financial condition.

Risks Related to Weather, Other Natural Phenomena and Business Disruption

Our assets and operations, as well as our customers’ assets and operations, can be affected by weather and other natural phenomena.

Our assets and operations, especially those located offshore, and our customers’ assets and operations can be adversely affected by hurricanes, floods, earthquakes, landslides, tornadoes and other natural phenomena and weather conditions, including extreme or unseasonable temperatures, making it more difficult for us to realize the historic rates of return associated with our assets and operations. A significant disruption in our or our customers’ operations or the occurrence of a significant liability for which we were not fully insured could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Our business could be negatively impacted by acts of terrorism and security threats, including cybersecurity threats, and related disruptions.

Given the volatile nature of the commodities we transport and store, our assets and the assets of our customers and others in our industry may be targets of terrorist activities. A terrorist attack could create significant price volatility, disrupt our business, limit our access to capital markets, or cause significant harm to our operations, such as full or partial disruption to our ability to transport natural gas. Acts of terrorism, as well as events occurring in response to or in connection with acts of terrorism, could cause environmental repercussions that could result in a significant decrease in revenues or significant reconstruction or remediation costs, which could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We rely on our information technology infrastructure to process, transmit and store electronic information, including information we use to safely operate our assets. While we believe that we maintain appropriate information security policies and protocols, we face cybersecurity and other security threats to our information technology infrastructure, which could include threats to our operational industrial control systems and safety systems that operate our pipelines, plants and assets. We could face unlawful attempts to gain access to our information technology infrastructure, including coordinated attacks from hackers, whether state-sponsored groups, “hacktivists,” or private individuals. The age, operating systems or condition of our current information technology infrastructure and software assets and our ability to maintain and upgrade such assets could affect our ability to resist cybersecurity threats. We could also face attempts to gain access to information related to our assets through attempts to obtain unauthorized access by targeting acts of deception against individuals with legitimate access to physical locations, or information. Breaches in our information technology infrastructure or physical facilities, or other disruptions including those arising from theft, vandalism, fraud, or unethical conduct, could result in damage to our assets, unnecessary waste, safety incidents, damage to the environment, reputational damage, potential liability or the loss of contracts, and have a material adverse effect on our operations, financial condition, results of operations, and cash flows.

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Item 1B.Unresolved Staff Comments

None.

Item 2. Properties

Our gas pipeline facilities are generally owned in fee. However, a substantial portion of such facilities are constructed and maintained pursuant to rights-of-way, easements, permits, licenses or consents on and across real property owned by others. Compressor stations, with appurtenant facilities, are located in whole or in part either on lands owned or on sites held under leases or permits issued or approved by public authorities. Our storage facilities are either owned or contracted for under long-term leases or easements. We lease our company offices in Houston, Texas.

Item 3. Legal Proceedings

Environmental

On May 5, 2017, we entered into a Consent Order with the Georgia Department of Natural Resources, Environmental Protection Division (GEPD) pertaining to alleged violations of the Georgia Water Quality Control Act and associated rules arising from a permit issued by GEPD for construction of the Dalton Project. Pursuant to the Consent Order, we paid a fine of $168,750 and agreed to perform a Corrective Action Order to remedy the alleged violations.

Other

The additional information called for by this item is provided in “Item 8. Financial Statements and Supplementary Data – Notes to Consolidated Financial Statements – Note 2. Contingent Liabilities and Commitments”.

Item 4. Mine Safety Disclosures

Not applicable.

PART II

Item 5.Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

We are indirectly owned by WPZ, which is consolidated by Williams. In January 2017, Williams permanently waived the WPZ general partner's incentive distribution rights, converted its 2 percent general partner interest in WPZ to a non-economic interest and purchased additional WPZ common units. At December 31, 2017, Williams owns a 74 percent limited partner interest in WPZ.

Distributions totaling $430 million were declared and paid by us to our parent during the year ended December 31, 2017. Distributions totaling $440 million were declared and paid by us to our parent during the year ended December 31, 2016. During July 2017, we recognized a non-cash distribution to our parent of $240 million.

In the year ended December 31, 2017, our parent made contributions totaling $410 million to us to fund a portion of our expenditures for additions to property, plant and equipment. In the year ended December 31, 2016, our parent made contributions to us totaling $502 million.

Item 6. Selected Financial Data

Since we meet the conditions set forth in General Instruction (I)(1)(a) and (b) of Form 10-K, this information is omitted.

21

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

General

The following discussion and analysis of critical accounting estimates, results of operations and capital resources and liquidity should be read in conjunction with the financial statements and notes thereto included within Item 8.

Critical Accounting Estimates

Our financial statements reflect the selection and application of accounting policies that require management to make significant estimates and assumptions. We believe that the following are the most critical judgment areas in the application of accounting policies that currently affect our financial condition and results of operations.

Regulatory Accounting

We are regulated by the FERC. The Accounting Standards Codification (ASC) Topic 980, Regulated Operations (Topic 980) provides that rate-regulated public utilities account for and report regulatory assets and liabilities consistent with the economic effect of the way in which regulators establish rates if the rates established are designed to recover the costs of providing the regulated service and if the competitive environment makes it probable that such rates can be charged and collected. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, employee related benefits, environmental costs, negative salvage, asset retirement obligations and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980 and, accordingly, the accompanying consolidated financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements. Management’s assessment of the probability of recovery or pass through of regulatory assets and liabilities requires judgment and interpretation of laws and regulatory commission orders. If, for any reason, we cease to meet the criteria for application of regulatory accounting treatment for all or part of our operations, the regulatory assets and liabilities related to those portions ceasing to meet such criteria would be eliminated from the Consolidated Balance Sheet and included in the Consolidated Statement of Comprehensive Income for the period in which the discontinuance of regulatory accounting treatment occurs, unless otherwise required to be recorded under other provisions of U.S. generally accepted accounting principles. The aggregate amount of regulatory assets reflected in the Consolidated Balance Sheet is $373.5 million at December 31, 2017. The aggregate amount of regulatory liabilities reflected in the Consolidated Balance Sheet is $1,007.1 million at December 31, 2017. A summary of regulatory assets and liabilities is included in Note 9 of Notes to Consolidated Financial Statements.

In December 2017, Tax Reform was enacted, which, among other things, reduced the federal corporate income tax rate from 35 percent to 21 percent. Rates charged to our customers permit the recovery of an income tax allowance that includes a deferred income tax component. As a result of the reduced income tax rate from Tax Reform and the collection of historical rates that reflected historical federal income tax rates, we expect that we will be required to return amounts to certain customers through future rates and have established a regulatory liability accordingly. The liability was recorded in December 2017 through a regulatory charge to operating income of $471.1 million (See Note 1). The timing and actual amount of such return will be subject to future negotiations regarding this matter and many other elements of cost-of-service rate proceedings, including other costs of providing services.

Our estimation of these regulatory liabilities incorporated the following significant judgments and assumptions involving income taxes collected from our customers:

• We utilized current FERC guidance for the default income tax rate for non-corporate taxpayers, which is an element of our overall effective tax rate. It is possible that the FERC will provide updated implementation guidance in the future, including an updated default income tax rate for non-corporate taxpayers. We estimate that a decline of one percentage point in our assumed overall effective tax rate would increase our regulatory liability by approximately $29 million.

22

• We made assumptions regarding the allocation of our taxable income between corporate and non-corporate taxpayers. This allocation is subject to annual variation that could impact the weighted average federal tax component of the overall income tax allowance rate.

• We made assumptions regarding the allocation of our taxable income among the states in which we conduct business. This allocation is subject to annual variation that could impact the weighted average state tax component of the overall income tax allowance rate. It is possible that certain states may change their income tax laws and/or rates in the future in response to Tax Reform.

• In determining the estimated liability that we currently believe is probable of return to customers through future rates, we considered the mix of services provided by us, taking into consideration that certain of these services are provided under contractually based rates, in lieu of recourse-based rates, that are designed to recover the cost of providing those services, with no expected future rate adjustment for the term of those contracts. We estimate that a one percent change in the relative mix of services would change the regulatory liability by approximately $8 million.

The use of alternative judgments and assumptions could result in the recognition of different regulatory liability and associated charges in the consolidated financial statements.

Certain of our equity-method investees recorded similar regulatory liabilities, for which our Equity in (earnings) loss of unconsolidated affiliates on our Consolidated Statement of Comprehensive Income has been reduced by $10.3 million associated with our proportionate share of the associated regulatory charges.

Our regulatory asset associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $32.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net on our Consolidated Statement of Comprehensive Income.

Impairment of Long-lived Assets

We evaluate our long lived assets for impairment when events or changes in circumstances indicate, in our management's judgment, that the carrying value of such assets may not be recoverable. When an indicator of a potential impairment has occurred, we compare our management's estimate of undiscounted future cash flows attributable to the assets to the carrying value of the assets to determine whether an impairment has occurred.

In December 2010 we detected a leak in one of the seven underground natural gas storage caverns at our Eminence Storage Field in Covington County, Mississippi. Due to the leak at this cavern, damage to the well at an adjacent cavern, and operating problems at two other caverns constructed at about the same time, we determined that the four caverns should be retired, which was completed in 2014. In addition, further studies have indicated the need for capital improvements over the next several years of the remaining three caverns. As a result, we performed an assessment of our Eminence storage field for impairment as of December 31, 2017. The carrying value at that date was $97 million. These events have not affected the performance of our obligations under our service agreements with our customers. However, judgments and assumptions are inherent in our estimate of future cash flows used to evaluate Eminence. In our evaluation, our estimate of the undiscounted cash flows of Eminence exceeded its carrying value, and thus no impairment loss was recognized in 2017. If our estimates of revenues were to significantly decrease, it could result in an impairment of this asset.

Results of Operations

Analysis of Financial Results

This analysis discusses financial results of our operations for the years 2017 and 2016. Variances due to changes in natural gas prices and transportation volumes have little impact on revenues, because under our rate design methodology, the majority of overall cost of service is recovered through firm capacity reservation charges in our transportation rates.

23

2017 COMPARED TO 2016

Operating Income and Net Income

Operating Income for 2017 was $153.9 million compared to $599.1 million for 2016. The decrease in Operating Income of $445.2 million (74.3 percent) was primarily due to an increase in Operating Costs and Expenses in 2017 compared to 2016, as discussed below, partly offset by higher Natural gas transportation and Natural gas storage revenues in 2017 compared to 2016, as discussed below. Net Income for 2017 was $55.7 million compared to $523.4 million for 2016. The decrease in Net Income of $467.7 million (89.4 percent) was mostly attributable to a decrease in Operating Income, as discussed below, and an unfavorable change in Other (Income) and Other Expenses, as discussed below.

Sales Revenues

We have cash out sales, which settle gas imbalances with shippers. In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. Additionally, we transport gas on various pipeline systems, which may deliver different quantities of gas on our behalf than the quantities of gas received from us. These transactions result in gas transportation and exchange imbalance receivables and payables. Our tariff includes a method whereby the majority of transportation imbalances are settled on a monthly basis through cash out sales or purchases. The cash out sales have no impact on our operating income or results of operations.

Operating Revenues

Natural gas sales increased $12.4 million (14.3 percent) to $99.1 million for 2017 when compared to 2016. The increase was primarily due to $8.3 million higher system management gas sales and $5.5 million higher cash-out sales. System management gas and cash-out sales are offset in our costs of natural gas sold and therefore had no impact on our operating income or results of operations.

Natural gas transportation for 2017 was $1,531.8 million compared to $1,397.3 million for 2016. The $134.5 million (9.6 percent) increase was primarily attributable to:

• $149.6 million increase in transportation reservation revenues related to new incremental projects primarily attributable to:

•$52.9 million from our Gulf Trace project placed in service in February 2017:

• $45.9 million from our Dalton project placed in partial service in April 2017, and fully in service in August 2017;

• $23.2 million from our Hillabee project Phase I placed in partial service in June 2017, and fully in service in July 2017;

•$9.6 million from our Atlantic Sunrise project placed in partial service in September 2017;

•$8.3 million from our Rock Spring project placed in service in August 2016;

•$5.5 million from our New York Bay expansion project placed in service in October 2017; and

•$3.4 million from our Virginia Southside Phase II project placed in service in December 2017.

• Partially offset by $6.2 million lower commodity revenues;

• $4.5 million lower firm transportation backhaul revenues; and

• $3.6 million due to one less billable day in 2017 compared to 2016.

Natural gas storage for 2017 was $137.3 million compared to $122.6 million for 2016. The $14.7 million (12.0 percent) increase was primarily due to the absence of an accrual for Washington Storage Service refunds recorded in 2016.

24

Operating Costs and Expenses

Excluding the Cost of natural gas sales, which is directly offset in revenues, our operating expenses increased approximately $591.7 million (63.6 percent) from the comparable period in 2016. This increase was primarily attributable to:

• A $471.1 million increase in Regulatory charges resulting from Tax Reform (Note 1);

• A $6.5 million (11.4 percent) increase in Other expense, net primarily related to an unfavorable change in the deferral of Asset Retirement Obligations (ARO) related depreciation to a regulatory asset;

• An $84.9 million (26.8 percent) increase in Operation and maintenance costs mostly due to $59.2 million higher costs due to pipeline integrity, general maintenance and other testing on our pipeline, and higher employee labor and related benefit costs of $15.2 million, of which, $7.6 million was related to a pension early payout program;

• A $13.3 million (7.9 percent) increase in Administrative and general costs primarily due to higher allocated corporate expenses;

• A $10.4 million (3.4 percent) increase in Depreciation and amortization costs primarily due to $19.8 million higher expense related to additional assets placed into service, partly offset by $10.2 million lower expenses due to ARO related depreciation; and

• A $5.5 million (9.2 percent) increase in Taxes-other than income taxes primarily due to higher ad valorem taxes as a result of additional assets placed into service.

Other (Income) and Other Expenses

Other (Income) and Other Expenses in 2017 had an unfavorable change of $22.5 million (29.7 percent) over 2016. This unfavorable change was primarily attributable to:

• A $27.7 million (748.6 percent) unfavorable change in Miscellaneous other (income) expenses, net primarily due to $32.7 million related to a regulatory asset charge associated with Tax Reform for the effects of deferred taxes on equity funds used during construction, partly offset by $5.1 million due to certain project related tax reimbursements;

• a $12.1 million (205.1 percent) unfavorable change in Equity in (earnings) loss of unconsolidated affiliates primarily related to a regulatory charge associated with establishing a regulatory liability resulting from Tax Reform;

• A $7.6 million (5.0 percent) unfavorable change in Interest expense-other primarily related to $10.1 million associated with an other financing obligation (See Note 3), partly offset by the absence of $2.9 million for our Washington Storage Service refunds recorded in 2016; and

• Partially offset by a $23.0 million (33.3 percent) favorable change in Allowance for equity and borrowed funds used during construction (AFUDC) associated with capital expenditures on projects.

Station 62 Incident

On October 8, 2015, an explosion and fire occurred at our Compressor Station No. 62 in Gibson, Louisiana. At the time of the incident, planned facility maintenance was being performed at the station and the facility was not operational. The incident was related to maintenance work being performed on the slug catcher at the station. Four contractor employees were killed in the incident and others were injured.

In responding to the incident, we cooperated with local, state and federal authorities, including the Louisiana State Police, Terrebonne Parish, the Louisiana Department of Environmental Quality, the U.S. Environmental Protection Agency (Region 6), the Occupational Safety and Health Administration, and the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA). On July 29, 2016, PHMSA issued a Notice of Probable Violation (NOPV), which includes a $1.6 million proposed civil penalty to us in connection with the incident. This penalty was accrued in the second quarter of 2016 and would not be covered by our insurance policies. We filed a response to the NOPV on August 25, 2016, and on July 14, 2017, PHMSA held a hearing on the NOPV.

The incident did not cause any rupture of the gas pipeline or any damage to the building containing the compressor engines. In anticipation of the planned maintenance, our Southeast Louisiana Lateral was taken out of service on

25

October 4, 2015, which affected approximately 200 MMcf/d of natural gas production. The lateral was restored to service in early 2016 after repairs were made to the facilities damaged in the incident.

We are a defendant in lawsuits seeking damages for wrongful death, personal injury and property damages. We believe it is reasonably possible that losses will be incurred on some lawsuits. However, in management's judgment, the ultimate resolution of these matters will not have a material effect on our financial condition, results of operations or cash flows. While we also have claims for indemnification, we believe that it is probable that any ultimate losses incurred will be covered by our general liability insurance policy.

Effects of Inflation

We have generally experienced increased costs due to the effect of inflation on the cost of labor, materials and supplies, and property, plant and equipment. A portion of the increased labor and materials and supplies cost can directly affect income through increased operation and maintenance expenses. The cumulative impact of inflation over a number of years has resulted in increased costs for current replacement of productive facilities. The majority of our property, plant and equipment and material and supplies inventory is subject to ratemaking treatment, and under current FERC practices, recovery is limited to historical costs. We believe that we will be allowed to recover and earn a return based on increased actual costs incurred when existing facilities are replaced. Cost based regulation along with competition and other market factors limit our ability to price services or products based upon inflation’s effect on costs.

CAPITAL RESOURCES AND LIQUIDITY

Method of Financing

We fund our capital requirements with cash flows from operating activities, equity contributions from WPZ, collection of advances to WPZ, accessing capital markets, and, if required, borrowings under the credit facility described below and advances from WPZ.

We may raise capital through private debt offerings, as well as offerings registered pursuant to offering-specific registration statements. Interest rates, market conditions, and industry conditions will affect amounts raised, if any, in the capital markets. On January 22, 2016, we completed a private placement of $1 billion in aggregate principal amount of 7.85 percent senior unsecured notes due 2026. We used the net proceeds from the offering to repay indebtedness, including our $200 million of 6.4 percent notes due upon their maturity on April 15, 2016, and to fund capital expenditures. The notes issued in January 2016 were the subject of a registration rights agreement. In January 2017, we completed an exchange of these notes for substantially identical new notes that are registered under the Securities Act.

We, along with WPZ and Northwest Pipeline LLC, are co-borrowers under a $3.5 billion unsecured credit facility. Total letter of credit capacity available to WPZ under the credit facility is $1.125 billion. We may borrow up to $500 million under the credit facility to the extent not otherwise utilized by WPZ and Northwest Pipeline LLC. See Note 3 of Notes to Consolidated Financial Statements for further discussion of the credit facility.

We are a participant in WPZ's cash management program, and we make advances to and receive advances from WPZ. At December 31, 2017, our advances to WPZ totaled approximately $395.2 million. These advances are represented by demand notes. The decrease in 2017 of these advances primarily resulted from the use of funds for capital expenditures.

Through wholly-owned subsidiaries, we hold a 35 percent interest in Pine Needle and approximately a 45 percent interest in Cardinal, which have interest rate swap agreements that qualify as cash flow hedge transactions under the accounting and reporting standards established by ASC Topic 815, Derivatives and Hedging. As such, our equity interest in the changes in fair value of Pine Needle’s hedge and Cardinal’s hedge are recognized in other comprehensive income.

Capital Expenditures

We categorize our capital expenditures as either maintenance capital expenditures or expansion capital expenditures. Maintenance capital expenditures are those expenditures required to maintain the existing operating capacity and service capability of our assets, including replacement of system components and equipment that are worn,

26

obsolete, completing their useful life, or necessary to remain in compliance with environmental laws and regulations. Expansion capital expenditures improve the service capability of existing assets, extend useful lives, increase transmission or storage capacities from existing levels, reduce costs or enhance revenues. We anticipate 2018 capital expenditures will be approximately $1.8 billion. Of this total, approximately $1.7 billion is considered nondiscretionary due to legal, regulatory, and/or contractual requirements, primarily due to expansion projects.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

At December 31, 2017, our debt portfolio included only fixed rate issues. The following table provides information about our long-term debt, including current maturities, as of December 31, 2017. The table presents principal cash flows and weighted-average interest rates by expected maturity dates.

December 31, 2017	Expected Maturity Date
	2018			2019			2020			2021
	(Dollars in millions)
Long-term debt, excluding other financing obligation:
Fixed rate	$	250		$	—		$	—		$	—
Interest rate	6.61		%	6.64		%	6.64		%	6.64		%
Other financing obligation:
Fixed rate	$	2		$	2		$	2		$	2
Interest rate	9.53		%	9.53		%	9.53		%	9.53		%
December 31, 2017	Expected Maturity Date
	2022			Thereafter			Total			Fair Value
	(Dollars in millions)
Long-term debt, excluding other financing obligation:
Fixed rate	$	—		$	1,983		$	2,233		$	2,653
Interest rate	6.64		%	5.49		%
Other financing obligation:
Fixed rate	$	2		$	221		$	231		$	450
Interest rate	9.53		%	9.53		%

27

Item 8. Financial Statements and Supplementary Data

	Page
Report of Independent Registered Public Accounting Firm	29
Consolidated Statement of Comprehensive Income	30
Consolidated Balance Sheet	31
Consolidated Statement of Member’s Equity	33
Consolidated Statement of Cash Flows	34
Notes to Consolidated Financial Statements	36

28

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To The Management Committee and Member of Transcontinental Gas Pipe Line Company, LLC

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheet of Transcontinental Gas Pipe Line Company, LLC (the Company) as of December 31, 2017 and 2016, and the related consolidated statements of comprehensive income, member’s equity, and cash flows for each of the three years in the period ended December 31, 2017, and the related notes (collectively referred to as the "consolidated financial statements"). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2017 and 2016, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2017, in conformity with U.S. generally accepted accounting principles.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company's financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company's internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

/s/ ERNST & YOUNG LLP

We have served as the Company's auditor since 1995.

Houston, Texas

February 22, 2018

29

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
Operating Revenues:
Natural gas sales	$	99,100		$	86,720		$	125,774
Natural gas transportation	1,531,778			1,397,341			1,318,656
Natural gas storage	137,348			122,555			137,983
Other	6,779			9,519			10,106
Total operating revenues	1,775,005			1,616,135			1,592,519
Operating Costs and Expenses:
Cost of natural gas sales	99,100			86,720			125,774
Cost of natural gas transportation	19,589			19,689			26,501
Operation and maintenance	401,871			316,989			288,386
Administrative and general	182,121			168,759			179,489
Depreciation and amortization	318,058			307,707			277,850
Taxes — other than income taxes	65,612			60,119			49,567
Regulatory charge resulting from Tax Reform (Note 1)	471,096			—			—
Other expense, net	63,644			57,064			57,800
Total operating costs and expenses	1,621,091			1,017,047			1,005,367
Operating Income	153,914			599,088			587,152
Other (Income) and Other Expenses:
Interest expense - affiliate	60			60			64
- other	158,814			151,234			82,774
Interest income - affiliate	(3,507		)	(2,201		)	(28		)
- other	(2,782		)	(2,185		)	(1,933		)
Allowance for equity and borrowed funds used during construction (AFUDC)	(92,013		)	(68,964		)	(63,072		)
Equity in (earnings) loss of unconsolidated affiliates	6,188			(5,914		)	(5,593		)
Miscellaneous other (income) expenses, net	31,426			3,683			(517		)
Total other (income) and other expenses	98,186			75,713			11,695
Net Income	55,728			523,375			575,457
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes $103, $167, and $316 for the years ended December 31, 2017, 2016, and 2015, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	327			41			84
Comprehensive Income	$	56,055		$	523,416		$	575,541

See accompanying notes.

30

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED BALANCE SHEET

(Thousands of Dollars)

	December 31,
	2017		2016
ASSETS
Current Assets:
Cash	$	—	$	—
Receivables:
Trade	167,928		141,726
Affiliates	1,109		489
Advances to affiliate	395,247		811,693
Other	2,494		2,589
Transportation and exchange gas receivables	3,205		1,827
Inventories:
Gas in storage, at original cost	790		786
Gas available for customer nomination, at average cost	1,850		17,233
Materials and supplies, at lower of average cost or market	37,387		37,190
Regulatory assets	97,149		87,059
Other	12,508		13,305
Total current assets	719,667		1,113,897
Investments, at cost plus equity in undistributed earnings	28,505		42,403
Property, Plant and Equipment:
Natural gas transmission plant	13,771,183		11,996,454
Less-Accumulated depreciation and amortization	3,859,520		3,687,473
Total property, plant and equipment, net	9,911,663		8,308,981
Other Assets:
Regulatory assets	276,315		264,001
Other	141,786		102,198
Total other assets	418,101		366,199
Total assets	$	11,077,936	$	9,831,480

(continued)

See accompanying notes.

31

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED BALANCE SHEET

(Thousands of Dollars)

	December 31,
	2017		2016
LIABILITIES AND MEMBER’S EQUITY
Current Liabilities:
Payables:
Trade	$	444,021	$	211,829
Affiliates	43,420		29,455
Cash overdrafts	25,132		40,043
Transportation and exchange gas payables	2,121		1,571
Accrued liabilities:
Property and other taxes	12,843		13,594
Interest	49,900		49,900
Regulatory liabilities	16,350		9,120
Customer deposits	15,754		47,049
Customer advances	44,689		34,923
Asset retirement obligations	13,676		26,934
Other	20,390		16,177
Long-term debt due within one year	251,430		—
Total current liabilities	939,726		480,595
Long-Term Debt	2,191,576		2,210,754
Other Long-Term Liabilities:
Asset retirement obligations	350,280		248,518
Regulatory liabilities	990,702		449,391
Advances for construction costs	426,771		283,028
Transportation prepayments	10,871		11,837
Deferred revenue	225,858		—
Other	4,828		6,088
Total other long-term liabilities	2,009,310		998,862
Contingent Liabilities and Commitments (Note 2)
Member’s Equity:
Member’s capital	4,088,499		3,678,499
Retained earnings	1,848,488		2,462,760
Accumulated other comprehensive income	337		10
Total member’s equity	5,937,324		6,141,269
Total liabilities and member’s equity	$	11,077,936	$	9,831,480

See accompanying notes.

32

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED STATEMENT OF MEMBER’S EQUITY

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
Member's Capital:
Balance at beginning of period	$	3,678,499		$	3,176,499		$	2,524,499
Cash contributions from parent	410,000			502,000			652,000
Balance at end of period	4,088,499			3,678,499			3,176,499
Retained Earnings:
Balance at beginning of period	2,462,760			2,379,385			2,339,928
Net income	55,728			523,375			575,457
Cash distributions to parent	(430,000		)	(440,000		)	(536,000		)
Non-cash distribution to parent	(240,000		)	—			—
Balance at end of period	1,848,488			2,462,760			2,379,385
Accumulated Other Comprehensive Income (Loss):
Balance at beginning of period	10			(31		)	(115		)
Equity interest in unrealized gain (loss) on interest rate hedge	327			41			84
Balance at end of period	337			10			(31		)
Total Member's Equity	$	5,937,324		$	6,141,269		$	5,555,853

See accompanying notes.

33

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED STATEMENT OF CASH FLOWS

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
Cash flows from operating activities:
Net income	$	55,728		$	523,375		$	575,457
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	318,058			307,707			277,850
Allowance for equity funds used during construction (equity AFUDC)	(69,653		)	(56,468		)	(48,435		)
Regulatory charge resulting from Tax Reform (Note 1)	471,096			—			—
Changes in operating assets and liabilities:
Receivables — affiliates	(620		)	595			(430		)
— trade and other	(26,107		)	5,941			(19,521		)
Transportation and exchange gas receivable	(1,378		)	600			1,058
Regulatory assets - current	(10,090		)	(7,484		)	(1,765		)
Regulatory assets - non-current	(10,761		)	(271		)	(24,650		)
Inventories	15,182			1,632			9,858
Payables — affiliates	12,514			(10,909		)	2,676
— trade	(9,823		)	29,375			(2,077		)
Accrued liabilities	(29,651		)	74,759			(10,015		)
Asset retirement obligations - non-current	103,105			31,114			19,022
Asset retirement obligation - removal costs	(4,578		)	(4,911		)	(3,097		)
Deferred revenue	(4,542		)	—			—
Other, net	14,415			32,030			45,007
Net cash provided by operating activities	822,895			927,085			820,938
Cash flows from financing activities:
Proceeds from long-term debt	—			998,250			—
Retirement of long-term debt	—			(200,000		)	—
Payments on other financing obligations	(486		)	—			—
Payments for debt issuance costs	(13		)	(8,381		)	—
Cash distributions to parent	(430,000		)	(440,000		)	(536,000		)
Cash contributions from parent	410,000			502,000			652,000
Net cash provided by (used in) financing activities	(20,499		)	851,869			116,000

(continued)

See accompanying notes.

34

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

CONSOLIDATED STATEMENT OF CASH FLOWS

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
Cash flows from investing activities:
Property, plant and equipment additions, net of equity AFUDC*	$	(1,576,611	)	$	(1,213,969	)	$	(1,270,860	)
Contributions and advances for construction costs	425,397			216,447			85,901
Disposal of property, plant and equipment, net	(49,090		)	(12,529		)	(12,358		)
Advances to affiliate, net	416,446			(747,085		)	242,302
Return of capital from unconsolidated affiliates	3,926			2,767			2,015
Purchase of ARO Trust investments	(57,099		)	(70,901		)	(64,087		)
Proceeds from sale of ARO Trust investments	31,435			44,195			43,284
Proceeds from insurance	3,200			2,121			35,132
Other, net	—			—			1,560
Net cash used in investing activities	(802,396		)	(1,778,954		)	(937,111		)
Increase (decrease) in cash	—			—			(173		)
Cash at beginning of period	—			—			173
Cash at end of period	$	—		$	—		$	—
____________________________
*   Increase to property, plant and equipment, net of equity AFUDC	$	(1,784,254	)	$	(1,200,696	)	$	(1,222,292	)
Changes in related accounts payable and accrued liabilities	207,643			(13,273		)	(48,568		)
Property, plant and equipment additions, net of equity AFUDC	$	(1,576,611	)	$	(1,213,969	)	$	(1,270,860	)
Supplemental disclosures of cash flow information:
Cash paid during the year for:
Interest (exclusive of amount capitalized)	$	136,439		$	103,391		$	66,489
Income taxes	2,089			828			1,161

See accompanying notes.

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TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Corporate Structure and Control

In this report, Transco (which includes Transcontinental Gas Pipe Line Company, LLC and, unless the context otherwise requires, all of our majority-owned subsidiaries) is at times referred to in the first person as “we,” “us” or “our.”

Transco is indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which is consolidated by The Williams Companies, Inc. (Williams). In January 2017, Williams permanently waived the WPZ general partner's incentive distribution rights, converted its 2 percent general partner interest in WPZ to a non-economic interest and purchased additional WPZ common units. At December 31, 2017, Williams owns a 74 percent limited partner interest in WPZ.

Transco is a single member limited liability company, and as such, single member losses are limited to the amount of its investment.

Related Party Transaction

A former member of Williams' Board of Directors, who was elected in 2013 and resigned during 2016, is also the current chairman, president, and chief executive officer of Public Service Enterprise Group, an energy services company that is a customers of ours. This board member does not have any material interest in any transactions between the energy services company and us and he had no role in any such transactions.

Nature of Operations

We are an interstate natural gas transmission company that owns a natural gas pipeline system extending from Texas, Louisiana, Mississippi and the Gulf of Mexico through Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, Pennsylvania and New Jersey to the New York City metropolitan area. The system serves customers in Texas and the 12 southeast and Atlantic seaboard states mentioned above, including major metropolitan areas in Georgia, Washington D.C., Maryland, North Carolina, New York, New Jersey and Pennsylvania.

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). The Accounting Standards Codification (ASC) Regulated Operations (Topic 980), provides that rate-regulated public utilities account for and report regulatory assets and liabilities consistent with the economic effect of the way in which regulators establish rates if the rates established are designed to recover the costs of providing the regulated service and if the competitive environment makes it probable that such rates can be charged and collected. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, employee related benefits, environmental costs, negative salvage, asset retirement obligations (ARO), and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980 and, accordingly, the accompanying consolidated financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

In December 2017, the Tax Cuts and Jobs Act was enacted, which, among other things, reduced the federal corporate income tax rate from 35 percent to 21 percent (Tax Reform). In accordance with ASC 980-740-25-2, we have recognized a regulatory liability to reflect the probable return to certain customers through future rates of the future decrease in income taxes payable associated with Tax Reform. In determining the estimated liability that we

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currently believe is probable of return to certain customers through future rates, we considered the mix of services provided by us, taking into consideration that certain of these services are provided under contractually based rates, in lieu of recourse-based rates, that are designed to recover the cost of providing those services, with no expected future rate adjustment for the term of those contracts. The liability was recorded in December 2017 through a regulatory charge to operating income of $471.1 million. The timing and actual amount of such return will be subject to future negotiations regarding this matter and many other elements of cost-of-service rate proceedings, including other costs of providing service.

Certain of our equity-method investees recorded similar regulatory liabilities, for which our Equity in (earnings) loss of unconsolidated affiliates on our Consolidated Statement of Comprehensive Income has been reduced by $10.3 million related to our proportionate share of the associated regulatory charges.

Our regulatory asset associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $32.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net on our Consolidated Statement of Comprehensive Income.

Basis of Presentation

Williams’ acquisition of Transco Energy Company and its subsidiaries, including us, in 1995 was accounted for using the purchase method of accounting. Accordingly, an allocation of the purchase price was assigned to our assets and liabilities based on their estimated fair values. The purchase price allocation to us primarily consisted of a $1.5 billion allocation to property, plant and equipment and adjustments to deferred taxes based upon the book basis of the net assets recorded as a result of the acquisition. The amount allocated to property, plant and equipment is being depreciated on a straight-line basis over 40 years, the estimated useful lives of these assets at the date of acquisition, at approximately $35 million per year. At December 31, 2017, the remaining property, plant and equipment allocation was approximately $0.6 billion. Current FERC policy does not permit us to recover through rates amounts in excess of original cost.

Principles of Consolidation

The consolidated financial statements include our accounts and the accounts of the subsidiaries we control. Companies in which we and our subsidiaries own 20 percent to 50 percent of the voting common stock or otherwise exercise significant influence over operating and financial policies of the company are accounted for under the equity method. The equity method investments as of December 31, 2017 and December 31, 2016 consist of Cardinal Pipeline Company, LLC (Cardinal) with ownership interest of approximately 45 percent and Pine Needle LNG Company, LLC (Pine Needle) with ownership interest of 35 percent. We received distributions associated with our equity method investments totaling $8.0 million, $8.6 million, and $7.6 million in 2017, 2016 and 2015, respectively. Included in the distributions are $3.9 million, $2.8 million and $2.0 million return of capital in 2017, 2016 and 2015, respectively.

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Estimates and assumptions which, in the opinion of management, are significant to the underlying amounts included in the financial statements and for which it would be reasonably possible that future events or information could change those estimates include: 1) revenues subject to refund; 2) litigation-related contingencies; 3) environmental remediation obligations; 4) impairment assessments of long-lived assets; 5) depreciation; 6) asset retirement obligations; and 7) regulatory deferred taxes.

Revenue Recognition

Revenues for transportation of gas under long-term firm agreements are recognized considering separately the reservation and commodity charges. Reservation revenues are recognized monthly over the term of the agreement regardless of the volume of natural gas transported. Commodity revenues from both firm and interruptible transportation are recognized in the period transportation services are provided based on volumes of natural gas physically delivered at the agreed upon delivery point. Revenues for the storage of gas under firm agreements are recognized considering separately the reservation, capacity, and injection and withdrawal charges. Reservation and capacity revenues are

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recognized monthly over the term of the agreement regardless of the volume of storage service actually utilized. Injection and withdrawal revenues are recognized in the period when volumes of natural gas are physically injected into or withdrawn from storage.

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. The resulting imbalances are primarily settled through the purchase and sale of gas with our customers under terms provided in our FERC tariff. Revenue is recognized from the sale of gas upon settlement of the transportation and exchange imbalances (See Gas Imbalances in this Note).

As a result of the ratemaking process, certain revenues collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel and other risks.

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that any expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

Property, Plant and Equipment

Property, plant and equipment is recorded at cost. The carrying values of these assets are also based on estimates, assumptions and judgments relative to capitalized costs, useful lives and salvage values. These estimates, assumptions and judgments reflect FERC regulations, as well as historical experience and expectations regarding future industry conditions and operations. The FERC identifies installation, construction and replacement costs that are to be capitalized. All other costs are expensed as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are credited or charged to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission facilities, production and gathering facilities and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC. Depreciation rates used for major regulated gas plant facilities at December 31, 2017, 2016 and 2015 are as follows:

Category of Property	2017-2015
Gathering facilities	1.35% - 2.50%
Storage facilities	2.10% -  2.25%
Onshore transmission facilities	2.61%  -  5.00%
Offshore transmission facilities	1.20%  -  1.20%

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurements of AROs include, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as a market-risk premium. The ARO asset is depreciated in a manner consistent with the expected timing of the future abandonment of the underlying physical assets. We measure changes in the liability due to passage of time by applying an interest method of allocation. The depreciation of the ARO asset and accretion of the ARO liability are recognized as an increase to a regulatory asset, as management expects to recover such amounts in future rates. The regulatory asset is amortized commensurate with our collection of these costs in rates.

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Impairment of Long-lived Assets

We evaluate the long lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. When an indicator of a potential impairment has occurred we compare our management’s estimate of undiscounted future cash flows attributable to the assets to the carrying value of the assets to determine whether an impairment has occurred. We apply a probability-weighted approach to consider the likelihood of different cash flow assumptions and possible outcomes including selling in the near term or holding for the remaining estimated useful life. If an impairment of the carrying value has occurred, we determine the amount of the impairment recognized in the financial statements by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

For assets identified to be disposed of in the future and considered held for sale in accordance with the ASC Property, Plant, and Equipment (Topic 360), we compare the carrying value to the estimated fair value less the cost to sell to determine if recognition of an impairment is required. Until the assets are disposed of, the estimated fair value, which includes estimated cash flows from operations until the assumed date of sale, is recalculated when related events or circumstances change.

Judgments and assumptions are inherent in our management’s estimate of undiscounted future cash flows used to determine recoverability of an asset and the estimate of an asset’s fair value used to calculate the amount of impairment to recognize.

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and are included as a cost of property, plant and equipment because it constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $22.3 million, $12.5 million and $14.6 million, for 2017, 2016 and 2015, respectively. The allowance for equity funds was $69.7 million, $56.5 million, and $48.4 million, for 2017, 2016 and 2015, respectively.

Income Taxes

We generally are not a taxable entity for federal or state and local income tax purposes. The tax on net income is generally borne by unitholders of our ultimate parent, WPZ. Net income for financial statement purposes may differ significantly from taxable income of WPZ’s unitholders as a result of differences between the tax basis and financial reporting basis of assets and liabilities and the taxable income allocation requirements under the WPZ partnership agreement. The aggregated difference in the basis of our assets for financial and tax reporting purposes cannot be readily determined because information regarding each of WPZ’s unitholder’s tax attributes in WPZ is not available to us.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts receivable are stated at the historical carrying amount net of reserves or write-offs. Our credit risk exposure in the event of nonperformance by the other parties is limited to the face value of the receivables. We perform ongoing credit evaluations of our customers’ financial condition and require collateral from our customers, if necessary. Due to our customer base, we have not historically experienced recurring credit losses in connection with our receivables. Receivables determined to be uncollectible are reserved or written off in the period of determination.

Gas Imbalances

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. Additionally, we transport gas on various pipeline systems which may deliver different quantities of gas on behalf of us than the quantities of gas received from us. These transactions result in gas transportation and exchange imbalance receivables and payables which are recovered or repaid in cash or through the receipt or delivery of gas in the future and are recorded in the accompanying Consolidated Balance Sheet. Settlement of imbalances requires agreement between the pipelines and shippers as to allocations of

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volumes to specific transportation contracts and timing of delivery of gas based on operational conditions. Our tariff includes a method whereby most transportation imbalances are settled on a monthly basis. Each month a portion of the imbalances are not identified to specific parties and remain unsettled. These are generally identified to specific parties and settled in subsequent periods. We believe that amounts that remain unidentified to specific parties and unsettled at year end are valid balances that will be settled with no material adverse effect upon our financial position, results of operations or cash flows. Management has implemented a policy of continuing to carry any unidentified transportation and exchange imbalances on the books for a three-year period. At the end of the three year period a final assessment will be made of their continued validity. Absent a valid reason for maintaining the imbalance, any remaining balance will be recognized in income. Certain imbalances are being recovered or repaid in cash or through the receipt or delivery of gas upon agreement of the parties as to the allocation of the gas volumes, and as permitted by pipeline operating conditions. These imbalances have been classified as current assets and current liabilities at December 31, 2017 and 2016. We utilize the average cost method of accounting for gas imbalances.

Deferred Cash Out

Most transportation imbalances are settled in cash on a monthly basis (cash out). We are required by our tariff to refund revenues received from the cash out of transportation imbalances in excess of costs incurred during the annual August through July reporting period. Revenues received in excess of costs incurred are deferred until refunded in accordance with the tariff.

Gas Inventory

We utilize the last-in, first-out (LIFO) method of accounting for inventory gas in storage. At December 31, 2017 and 2016, Gas in Storage, at LIFO, was zero. The basis for determining current cost at the end of each year is the December monthly average gas price delivered to pipelines in Texas and Louisiana. We utilize the average cost method of accounting for gas available for customer nomination. Liquefied natural gas in storage is valued at original cost.

Materials and Supplies Inventory

All inventories are stated at lower of average cost or net realizable value. We perform an annual review of Materials and Supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2017 and 2016.

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans. (See Note 6.) Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us and thus paid by us, is based on our share of net periodic benefit cost.

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Cash Flows from Operating Activities and Cash Equivalents

We use the indirect method to report cash flows from operating activities, which requires adjustments to net income to reconcile to net cash flows provided by operating activities. We include short-term, highly-liquid investments that have an original maturity of three months or less as cash equivalents.

Accounting Standards Issued But Not Yet Adopted

In August 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-15 “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15). ASU 2016-15 provides specific guidance on eight cash flow classification issues, including debt prepayment or debt extinguishment costs and distributions received from equity method investees, to reduce diversity in practice. ASU 2016-15 is effective for interim and annual periods beginning after December 15, 2017. Early adoption is permitted. ASU 2016-15 requires a retrospective transition. We do not expect ASU 2016-15 to have a material impact on our consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13 “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 changes the impairment model for most financial assets and certain other instruments. For trade and other receivables, held-to-maturity debt securities, loans, and other instruments, entities will be required to use a new forward-looking “expected loss” model that generally will result in the earlier recognition of allowances for losses. The guidance also requires increased disclosures. ASU 2016-13 is effective for interim and annual periods beginning after December 15, 2019. Early adoption is permitted. ASU 2016-13 requires varying transition methods for the different categories of amendments. We do not expect ASU 2016-13 to have a significant impact on our consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02 “Leases (Topic 842)” (ASU 2016-02). ASU 2016-02 establishes a comprehensive new lease accounting model. ASU 2016-02 modifies the definition of a lease, requires a dual approach to lease classification similar to current lease accounting, and causes lessees to recognize leases on the balance sheet as a lease liability measured as the present value of the future lease payments with a corresponding right-of-use asset, with an exception for leases with a term of one year or less. Additional disclosures will also be required regarding the amount, timing, and uncertainty of cash flows arising from leases. In January 2018, the FASB issued ASU 2018-01 “Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842” (ASU 2018-01). Per ASU 2018-01, land easements and rights-of-way are required to be assessed under ASU 2016-02 to determine whether the arrangements are or contain a lease and permits an entity to elect a transition practical expedient to not apply ASU 2016-02 to land easements that exist or expired before the effective date of ASU 2016-02 and that were not previously assessed under the previous lease guidance in ASC Topic 840 “Leases”. ASU 2016-02 is effective for interim and annual periods beginning after December 15, 2018. Early adoption is permitted. ASU 2016-02 currently requires a modified retrospective transition for financing or operating leases existing at or entered into after the beginning of the earliest comparative period presented in the financial statements.

In January 2018, the FASB proposed an accounting standard update titled “Leases (Topic 842): Targeted Improvements”, which is an update to ASU 2016-02 allowing entities an additional transition method to the existing requirements whereby an entity could adopt the provisions of ASU 2016-02 by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption without adjustment to the financial statements for periods prior to adoption. We expect to adopt ASU 2016-02 effective January 1, 2019. We are in the process of reviewing contracts to identify leases based on the modified definition of a lease, implementing a financial lease accounting system, and evaluating internal control changes to support management in the accounting for and disclosure of leasing activities. While we are still in the process of completing our implementation evaluation of ASU 2016-02, we currently believe the most significant changes relate to the recognition of a lease liability and offsetting right-of-use asset in our Consolidated Balance Sheet for operating leases. We are also evaluating ASU 2016-02's currently available and proposed practical expedients on adoption.

In May 2014, the FASB issued ASU 2014-09 establishing ASC Topic 606, “Revenue from Contracts with Customers” (ASC 606). ASC 606 establishes a comprehensive new revenue recognition model designed to depict the transfer of goods or services to a customer in an amount that reflects the consideration the entity expects to be entitled

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to receive in exchange for those goods or services and requires significantly enhanced revenue disclosures. In August 2015, the FASB issued ASU 2015-14 “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date” (ASU 2015-14). Per ASU 2015-14, the standard is effective for interim and annual reporting periods beginning after December 15, 2017. ASC 606 allows either full retrospective or modified retrospective transition and early adoption is permitted for annual periods beginning after December 15, 2016. We are adopting ASC 606 utilizing the modified retrospective transition approach, effective January 1, 2018. We do not anticipate any cumulative effect adjustment to retained earnings upon initially applying ASC 606 for periods prior to January 1, 2018.

We are in the final stages of evaluating the impact ASC 606 will have on our financial statements. For each revenue contract type, we have conducted a formal contract review process to evaluate the impact of ASC 606. We have substantially completed our evaluation. During the fourth quarter of 2017, we concluded on certain technical matters, including the evaluation of significant financing components and prepayments for services, resulting in no adjustment upon adoption. We continue to evaluate and develop disclosures required under the new standard, with a particular focus on the scope of contracts subject to disclosure of remaining performance obligations. Financial system and internal control changes necessary for adoption have been implemented effective as of January 1, 2018. We do not expect ASC 606 to have a material impact on the timing of our revenue recognition.

2. CONTINGENT LIABILITIES AND COMMITMENTS

Rate Matters

General rate case (Docket No. RP06-569) On August 31, 2006, we submitted to the FERC a general rate filing principally designed to recover increased costs. The rates became effective March 1, 2007, subject to refund and the outcome of a hearing. All issues in this proceeding except one were resolved by settlement.

The one issue reserved for litigation or further settlement related to our proposal to change the design of the rates for service under our WSS-OA storage rate schedule, which was implemented subject to refund on March 1, 2007. Following a hearing, the FERC issued an opinion approving our proposed incremental rate design, and subsequently denied requests for rehearing of that approval. On February 21, 2014, the U. S. Court of Appeals for the D.C. Circuit (D.C. Circuit) issued an opinion that vacated and remanded the FERC's order because the FERC did not adequately support its conclusions. On March 17, 2016, the FERC issued an order addressing the issues raised by the D.C. Circuit's opinion. In the March 17 order, the FERC reversed its prior opinion and found that Transco's incremental rate design was unjust and unreasonable. The FERC directed Transco to design its WSS-OA rates on a rolled-in basis, to file revised WSS-OA rates reflecting the findings in the order, and to refund the amounts collected in excess of those rates since March 1, 2007. On April 18, 2016, we submitted the compliance filing reflecting rolled-in rates for WSS-OA service consistent with the March 17 order, and began charging those rates beginning April 19, 2016. We also filed a request for rehearing of the March 17 order. On October 4, 2017, the FERC issued an order denying all requests for rehearing of the March 17 order, accepting our April 18, 2016 compliance filing, and directing us to make refunds. No party filed a request for rehearing of the October 4 order, and no party filed an appeal of the March 17, 2016 or October 4, 2017 order. On November 16, 2017, we issued refunds of $19.2 million to the affected customers.

The rates we charge to our customers are subject to the rate-making policies of the FERC. These policies permit us to include in our cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Reform, makes significant changes to the U.S. federal income tax rules applicable to both individuals and entities, including among other things, a reduction in corporate federal income tax rates. Although we expect that the decreased federal income tax rates will require us to return amounts to certain customers in the future and as a result we recognized a regulatory liability as of the date of enactment of Tax Reform, the details of any regulatory implementation guidance remain uncertain.

Station 62 Incident

On October 8, 2015, an explosion and fire occurred at our Compressor Station No. 62 in Gibson, Louisiana. At the time of the incident, planned facility maintenance was being performed at the station and the facility was not operational. The incident was related to maintenance work being performed on the slug catcher at the station. Four contractor employees were killed in the incident and others were injured.

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In responding to the incident, we cooperated with local, state and federal authorities, including the Louisiana State Police, Terrebonne Parish, the Louisiana Department of Environmental Quality, the U.S. Environmental Protection Agency (Region 6), the Occupational Safety and Health Administration, and the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA). On July 29, 2016, PHMSA issued a Notice of Probable Violation (NOPV), which includes a $1.6 million proposed civil penalty to us in connection with the incident. This penalty was accrued in the second quarter of 2016 and would not be covered by our insurance policies. We filed a response to the NOPV on August 25, 2016, and on July 14, 2017, PHMSA held a hearing on the NOPV.

The incident did not cause any rupture of the gas pipeline or any damage to the building containing the compressor engines. In anticipation of the planned maintenance, our Southeast Louisiana Lateral was taken out of service on October 4, 2015, which affected approximately 200 MMcf/d of natural gas production. The lateral was restored to service in early 2016 after repairs were made to the facilities damaged in the incident.

We are a defendant in lawsuits seeking damages for wrongful death, personal injury and property damages. We believe it is reasonably possible that losses will be incurred on some lawsuits. However, in management's judgment, the ultimate resolution of these matters will not have a material effect on our financial condition, results of operations or cash flows. While we also have claims for indemnification, we believe that it is probable that any ultimate losses incurred will be covered by our general liability insurance policy.

Environmental Matters

We have had studies underway for many years to test some of our facilities for the presence of toxic and hazardous substances such as polychlorinated biphenyls (PCBs) and mercury to determine to what extent, if any, remediation may be necessary. We have also similarly evaluated past on-site disposal of hydrocarbons at a number of our facilities. We have worked closely with and responded to data requests from the U.S. Environmental Protection Agency (EPA) and state agencies regarding such potential contamination of certain of our sites. On the basis of the findings to date, we estimate that environmental assessment and remediation costs under various federal and state statutes will total approximately $6 million to $8 million (including both expense and capital expenditures), measured on an undiscounted basis, and will substantially be spent over the next four to six years. This estimate depends on a number of assumptions concerning the scope of remediation that will be required at certain locations and the cost of the remedial measures. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs. At December 31, 2017, we had a balance of approximately $4.0 million for the expense portion of these estimated costs, $1.8 million recorded in Accrued liabilities - Other and $2.2 million recorded in Other Long-Term Liabilities - Other in the accompanying Consolidated Balance Sheet. At December 31, 2016, we had a balance of approximately $4.2 million for the expense portion of these estimated costs, $2.1 million recorded in Accrued liabilities - Other and $2.1 million recorded in Other Long-Term Liabilities - Other in the accompanying Consolidated Balance Sheet.

We have been identified as a potentially responsible party (PRP) at various Superfund and state waste disposal sites. Based on present volumetric estimates and other factors, our estimated aggregate exposure for remediation of these sites is less than $0.5 million. The estimated remediation costs for all of these sites are included in the $6 million to $8 million range discussed above. Liability under the Comprehensive Environmental Response, Compensation and Liability Act and applicable state law can be joint and several with other PRPs. Although volumetric allocation is a factor in assessing liability, it is not necessarily determinative; thus, the ultimate liability could be substantially greater than the amounts described above.

The EPA and various state regulatory agencies routinely promulgate and propose new rules, and issue updated guidance to existing rules. More recent rules and rulemakings include, but are not limited to, rules for reciprocating internal combustion engine maximum achievable control technology, air quality standards for one hour nitrogen dioxide emissions, and volatile organic compound and methane new source performance standards impacting design and operation of storage vessels, pressure valves, and compressors. On October 1, 2015, the EPA issued its rule regarding National Ambient Air Quality Standards for ground-level ozone, setting a stricter standard of 70 parts per billion. We are monitoring the rule’s implementation as the reduction will trigger additional federal and state regulatory actions that may impact our operations. Implementation of the regulations is expected to result in impacts to our operations and increase the cost of additions to Total property, plant and equipment, net in the Consolidated Balance Sheet for both new and existing facilities in affected areas. We are unable to reasonably estimate the cost of additions that may

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be required to meet the regulations at this time due to uncertainty created by various legal challenges to these regulations and the need for further specific regulatory guidance.

We consider prudently incurred environmental assessment and remediation costs and the costs associated with compliance with environmental standards to be recoverable through rates. To date, we have been permitted recovery of environmental costs, and it is our intent to continue seeking recovery of such costs through future rate filings. As a result, as estimated costs of environmental assessment and remediation are incurred, they are recorded as regulatory assets in the Consolidated Balance Sheet until collected through rates. At December 31, 2017, we had a balance of approximately $2.2 million of uncollected environmental related regulatory assets, $1.2 million recorded in Current Assets - Regulatory assets and $1.0 million recorded in Other Assets - Regulatory assets in the accompanying Consolidated Balance Sheet. At December 31, 2016, we had a balance of approximately $2.5 million of uncollected environmental related regulatory assets, $1.2 million recorded in Current Assets - Regulatory assets and $1.3 million recorded in Other Assets - Regulatory assets in the accompanying Consolidated Balance Sheet.

Other Matters

Various other proceedings are pending against us and are considered incidental to our operations.

Summary

We estimate that for all matters for which we are able to reasonably estimate a range of loss, including those noted above and others that are not individually significant, our aggregate reasonably possible losses beyond amounts accrued for all of our contingent liabilities are immaterial to our expected future annual results of operations, liquidity and financial position. These calculations have been made without consideration of any potential recovery from third parties. We have disclosed all significant matters for which we are unable to reasonably estimate a range of possible loss.

Other Commitments

Commitments for construction We have commitments for construction and acquisition of property, plant and equipment of approximately $114 million at December 31, 2017.

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3.DEBT, FINANCING ARRANGEMENTS AND LEASES

Long-Term Debt

At December 31, 2017 and 2016, long-term debt outstanding was as follows (in thousands):

	2017			2016
Debentures:
7.08% due 2026	$	7,500		$	7,500
7.25% due 2026	200,000			200,000
Total debentures	207,500			207,500
Notes:
6.05% due 2018	250,000			250,000
7.85% due 2026	1,000,000			1,000,000
5.4% due 2041	375,000			375,000
4.45% due 2042	400,000			400,000
Total notes	2,025,000			2,025,000
Other financing obligation	230,926			—
Total long-term debt, including current portion	2,463,426			2,232,500
Unamortized debt issuance costs	(15,377		)	(16,408		)
Unamortized debt premium and discount, net	(5,043		)	(5,338		)
Long-term debt due within one year	(251,430		)	—
Total long-term debt	$	2,191,576		$	2,210,754

Aggregate minimum maturities (face value) applicable to long-term debt outstanding at December 31, 2017, for the next five years, are as follows (in thousands):

2018:     6.05% Notes and other financing obligation	$	251,566
2019:     Other financing obligation	$	1,721
2020:     Other financing obligation	$	1,893
2021:     Other financing obligation	$	2,081
2022:     Other financing obligation	$	2,289

No property is pledged as collateral under any of our long-term debt issues.

Restrictive Debt Covenants

At December 31, 2017, none of our debt instruments restrict the amount of distributions to our parent, provided, however, that under the credit facility described below, we are restricted from making distributions to our parent during an event of default if we have directly incurred indebtedness under the credit facility. Our debt agreements contain restrictions on our ability to incur secured debt beyond certain levels and to guarantee certain indebtedness. The indenture governing our $1 billion of 7.85% Senior Notes due 2026 further restricts our ability to guarantee certain indebtedness.

Issuance and Retirement of Long-Term Debt

On January 22, 2016, we issued $1 billion of 7.85 percent senior unsecured notes due 2026 to investors in a private debt placement. A portion of these proceeds was used to retire our $200 million of 6.4 percent notes that matured on April 15, 2016. We used the remainder for funding of capital expenditures. As part of the new issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. We were obligated to file and consummate a registration statement for an offer to exchange the notes for a new issue of substantially identical notes registered under the Securities Act, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. In January

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2017, we completed an exchange of these notes for substantially identical new notes that are registered under the Securities Act.

Other Financing Obligation

During the construction of our Dalton Expansion Project, we received funding from a partner for its proportionate share of construction costs related to its undivided ownership interest in the Dalton lateral. Amounts received were recorded in Advances for construction costs and 100 percent of the costs associated with construction were capitalized on our Consolidated Balance Sheet. Upon placing the project in service during the third quarter of 2017, we began leasing this partner's undivided interest in the lateral, including the associated pipeline capacity, and reclassified approximately $235.8 million of funding previously received from our partner from Advances for construction costs to Long-Term Debt on our Consolidated Balance Sheet to reflect the financing obligation payable to our partner over an expected term of 35 years. At December 31, 2017, the amount included in Long-Term Debt on our Consolidated Balance Sheet for financing obligation is $229.4 million. As this transaction did not meet the criteria for sale leaseback accounting due to our continued involvement, it was accounted for as a financing arrangement over the course of the capacity agreement. The obligation matures in July 2052, requires monthly interest and principal payments, and bears an interest rate of approximately 10 percent.

Long-Term Debt Due Within One Year

The long-term debt due within one year at December 31, 2017 is associated with the $250 million of 6.05 percent notes maturing on June 15, 2018 and with the previously described other financing obligation.

Credit Facility

On February 2, 2015, we along with WPZ, Northwest, the lenders named therein and an administrative agent entered into the Second Amended & Restated Credit Agreement with aggregate commitments available of $3.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. In November 2017, the maturity date of the facility was extended to February 2, 2021. However, the co-borrowers may request an additional extension of the maturity date for a one year period to allow a maturity date as late as February 2, 2022, under certain circumstances. The agreement allows for swing line loans up to aggregate amount of $150 million, subject to available capacity under the credit facility, and letters of credit commitments available to WPZ of $1.125 billion. We are able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At December 31, 2017, no letters of credit have been issued and no loans to WPZ were outstanding under the credit facility.

Measured as of December 31, 2017, we are in compliance with our financial covenant under the credit facility.

Various covenants may limit, among other things, a borrower's and its material subsidiaries' ability to grant certain liens supporting indebtedness, merge or consolidate, sell all or substantially all of its assets, enter into certain affiliate transactions, make certain distributions during an event of default, enter into certain restrictive agreements, and allow any material change in the nature of its business.

If an event of default with respect to a borrower occurs under the credit facility, the lenders will be able to terminate the commitments for the respective borrowers and accelerate the maturity of any loans of the defaulting borrower under the credit facility agreement and exercise other rights and remedies.

Other than swing line loans, each time funds are borrowed, the borrower must choose whether such borrowing will be an alternate base rate borrowing or a Eurodollar borrowing. If such borrowing is an alternate base rate borrowing, interest is calculated on the basis of the greater of (a) the Prime Rate, (b) the Federal Funds Effective Rate plus one half of 1 percent and (c) a periodic fixed rate equal to the London Interbank Offered Rate (LIBOR) plus 1 percent, plus, in the case of each of (a), (b) and (c), an applicable margin. If the borrowing is a Eurodollar borrowing, interest is calculated on the basis of LIBOR for the relevant period plus an applicable margin. Interest on swing line loans is calculated as the sum of the alternate base rate plus an applicable margin. The borrower is required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin and the commitment fee are determined for each borrower by reference to a pricing schedule based on such borrower's senior unsecured long-term debt ratings.

WPZ participates in a commercial paper program and WPZ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. The program allows a maximum outstanding amount at any time of $3 billion of unsecured commercial paper notes. At December 31, 2017, WPZ had no outstanding commercial paper.

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Lease Obligations

The future minimum lease payments under our various operating leases are as follows (in thousands):

2018	$	13,558
2019	14,890
2020	14,860
2021	14,710
2022	14,654
Thereafter	122,333
Total net minimum obligations	$	195,005

Our lease expense was $11.0 million in 2017, $10.6 million in 2016, and $10.7 million in 2015.

4. ARO TRUST

Available-for-Sale Investments

We are entitled to collect in rates the amounts necessary to fund our ARO. We deposit monthly, into an external trust account (ARO Trust), the revenues specifically designated for ARO. The ARO Trust carries a moderate risk portfolio. We measure the financial instruments held in our ARO Trust at fair value. However, in accordance with the ASC Topic 980, Regulated Operations, both realized and unrealized gains and losses of the ARO Trust are recorded as regulatory assets or liabilities.

Effective March 1, 2013, the annual funding obligation is approximately $36.4 million, with deposits made monthly.

Investments in available-for-sale securities within the ARO Trust at fair value were as follows (in millions):

	December 31, 2017				December 31, 2016
	Amortized Cost Basis		Fair Value		Amortized Cost Basis		Fair Value
Cash and Money Market Funds	$	12.6	$	12.6	$	5.0	$	5.0
U.S. Equity Funds	35.9		50.5		29.4		36.5
International Equity Funds	20.7		24.6		19.2		18.6
Municipal Bond Funds	46.8		46.9		36.7		36.3
Total	$	116.0	$	134.6	$	90.3	$	96.4

5. FAIR VALUE MEASUREMENTS

The following table presents, by level within the fair value hierarchy, certain of our financial assets and liabilities. The carrying values of cash, short-term financial assets (advances to affiliate) that have variable interest rates, accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments. Therefore, these assets and liabilities are not presented in the following table.

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							Fair Value Measurements Using
	Carrying Amount			Fair Value			Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
							(Millions)
Assets (liabilities) at December 31, 2017:
Measured on a recurring basis:
ARO Trust investments	$	134.6		$	134.6		$	134.6	$	—		$	—
Additional disclosures:
Long-term debt, including current portion	(2,443.0		)	(3,103.3		)	—		(3,103.3		)	—
Assets (liabilities) at December 31, 2016:
Measured on a recurring basis:
ARO Trust investments	$	96.4		$	96.4		$	96.4	$	—		$	—
Additional disclosures:
Long-term debt	(2,210.8		)	(2,507.5		)	—		(2,507.5		)	—

Fair Value of Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

ARO Trust investments - We deposit a portion of our collected rates, pursuant to the terms of the Docket No. RP12-993 rate case settlement, into the ARO Trust which is specifically designated to fund future asset retirement obligations. The ARO Trust invests in a portfolio of actively traded mutual funds that are measured at fair value on a recurring basis based on quoted prices in an active market, are classified as available-for-sale and are reported in Other Assets-Other in the Consolidated Balance Sheet. However, both realized and unrealized gains and losses are ultimately recorded as regulatory assets or liabilities. See Note 4 for more information regarding the ARO Trust.

Long-term debt - The disclosed fair value of our long-term debt is determined primarily by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The fair value of the financing obligation associated with our Dalton lateral, which is included within long-term debt, was determined using an income approach (See Note 3 - Debt and Financing Agreements).

Reclassifications of fair value between Level 1, Level 2, and Level 3 of the fair value hierarchy, if applicable, are made at the end of each quarter. No transfers between Level 1 and Level 2 occurred during the year ended December 31, 2017 or 2016.

6. BENEFIT PLANS

Certain of the benefit costs charged to us by Williams associated with employees who directly support us are described below. Additionally, allocated corporate expenses from Williams to us also include amounts related to these same employee benefits, which are not included in the amounts presented below.

Pension and Other Postretirement Benefit Plans

Williams has noncontributory defined benefit pension plans (Williams Pension Plan, Williams Inactive Employees Pension Plan and The Williams Companies Retirement Restoration Plan) that provide pension benefits for its eligible employees. Pension cost charged to us by Williams was $15.6 million, $8.7 million and $13.5 million for 2017, 2016, and 2015, respectively. Included in our 2017 pension costs is a $7.6 million settlement charge. This amount reflects

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the portion of Williams’ settlement charge directly charged to us which was required as a result of lump-sum benefit payments made under Williams’ 2017 program to pay out certain deferred vested pension benefits, as well as lump-sum benefit payments made throughout 2017. In addition, we were charged $4.6 million of allocated corporate expenses also associated with the settlement charge.

Williams makes annual cash contributions to the pension plans, based on annual actuarial estimates, which Transco recovers through rates that are set through periodic general rate filings. Effective with the RP12-993 Settlement, any amounts of annual contributions that exceed an upper threshold or fall below a lower threshold are recorded as adjustments to income and collected or refunded through future rate adjustments. The amount of deferred pension collections recorded as a regulatory liability at December 31, 2017 and 2016 were $32.5 million and $21.3 million, respectively.

Williams provides subsidized retiree health care and life insurance benefits to certain eligible participants. Generally, participants that were employed by Williams on or before December 31, 1991 or December 31, 1995, if they were employees or retirees of Transco Energy Company and its subsidiaries, are eligible for subsidized retiree health care benefits. We recognized other postretirement benefit income of $10.9 million, $12.0 million and $11.9 million for 2017, 2016, and 2015, respectively.

We have been allowed by rate case settlements to collect or refund in future rates any differences between the actuarially determined costs and amounts currently being recovered in rates related to other postretirement benefits. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as an adjustment to expense and collected or refunded through future rate adjustments. The amount of other postretirement benefits costs deferred as a regulatory liability at December 31, 2017 and 2016 are $73.9 million and $63.0 million, respectively. These amounts are comprised of amounts being deferred for future rate treatment of $65.4 million and $52.0 million at December 31, 2017 and 2016, respectively, and amounts of $8.5 million and $11.0 million being amortized over a period of approximately 8 years per Docket No. RP12-993 at December 31, 2017 and 2016, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $7.7 million, $6.5 million and $6.6 million in 2017, 2016 and 2015, respectively, for Williams’ company matching contributions to this plan.

Employee Stock-Based Compensation Plan Information

The Williams Companies, Inc. 2007 Incentive Plan, as subsequently amended and restated, (Plan) provides for Williams’ common stock based awards to both employees and non-management directors. The Plan permits the granting of various types of awards including, but not limited to, restricted stock units and stock options. Awards may be granted for no consideration other than prior and future services or based on certain financial performance targets achieved.

Williams currently bills us directly for compensation expense related to stock-based compensation awards based on the fair value of the awards. We are also billed for our proportionate share of Williams’ and other affiliates’ stock-based compensation expense through various allocation processes.

Total stock-based compensation expense for the years ended December 31, 2017, 2016, and 2015 was $5.7 million, $4.0 million and $4.0 million, respectively, excluding amounts allocated from WPZ and Williams.

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7. TRANSACTIONS WITH MAJOR CUSTOMERS AND AFFILIATES

Major Customers

Operating revenues received from three of our major customers in 2017, 2016 and 2015 are as follows (in millions):

	2017		2016		2015
Duke Energy Corporation	$	198.4	$	178.9	$	94.6
National Grid	177.4		166.3		129.6
The Southern Company, Inc.	160.0		69.6		61.6

Affiliates

We are a participant in WPZ’s cash management program, and we make advances to and receive advances from WPZ. At December 31, 2017 and 2016, our advances to WPZ totaled approximately $395.2 million and $811.7 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate in the accompanying Consolidated Balance Sheet. Advances are stated at the historical carrying amounts. Interest income is recognized when chargeable and collectability is reasonably assured. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on WPZ’s excess cash at the end of each month. At December 31, 2017, the interest rate was 1.16 percent.

Included in Operating Revenuesin the accompanying Consolidated Statement of Comprehensive Income for 2017, 2016 and 2015 are revenues received from affiliates of $10.3 million, $11.2 million, and $4.6 million, respectively. The rates charged to provide sales and services to affiliates are the same as those that are charged to similarly-situated nonaffiliated customers.

Included in Cost of natural gas sales in the accompanying Consolidated Statement of Comprehensive Income for 2017, 2016 and 2015 is purchased gas cost from affiliates of $3.9 million, $4.3 million, and $6.0 million, respectively. All gas purchases are made at market or contract prices.

We have no employees. Services necessary to operate our business are provided to us by Williams and certain affiliates of Williams. We reimburse Williams and its affiliates for all direct and indirect expenses incurred or payments made (including salary, bonus, incentive compensation and benefits) in connection with these services. Employees of Williams also provide general, administrative and management services to us, and we are charged for certain administrative expenses incurred by Williams. These charges are either directly identifiable or allocated to our assets. Direct charges are for goods and services provided by Williams at our request. Allocated charges are based on a three-factor formula, which considers revenues; property, plant and equipment; and payroll. In management’s estimation, the allocation methodologies used are reasonable and result in a reasonable allocation to us of our costs of doing business incurred by Williams. We were billed $370.4 million, $318.4 million, and $327.1 million during 2017, 2016 and 2015, respectively, for these services. Such expenses are primarily included in Administrative and general and Operation and maintenance expenses in the accompanying Consolidated Statement of Comprehensive Income. The amount billed to us during 2016 includes $7.4 million for severance and other related costs associated with a reduction in workforce primarily recognized in the first quarter.

We provide services to certain of our affiliates. We recorded reductions in operating expenses for services provided to and reimbursed by our affiliates of $3.7 million, $4.3 million, and $5.7 million in 2017, 2016 and 2015, respectively.

We made equity distributions of $430 million, $440 million and $536 million during 2017, 2016 and 2015, respectively.

During 2017, 2016 and 2015, our parent made contributions totaling $410 million, $502 million and $652 million, respectively, to us to fund a portion of our expenditures for additions to property, plant and equipment.

During July 2017, we recorded deferred revenue and recognized a non-cash distributionto our parent of $240 million associated with funds received by WPZ related to the March 2016 WPZ agreement with the member-sponsors of Sabal Trail regarding the Hillabee Expansion and Sabal Trail projects. Although the agreement was between WPZ

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and the member-sponsors, since the agreement was, in part, related to furthering the completion of Hillabee, this deferred revenue is assigned to our results of operations over the 25-year term of the capacity agreement with Sabal Trail.

8. ASSET RETIREMENT OBLIGATIONS

These accrued obligations relate to underground storage caverns, offshore platforms, pipelines, and gas transmission facilities. At the end of the useful life of each respective asset, we are legally obligated to plug storage caverns and remove any related surface equipment, to dismantle offshore platforms, to cap certain gathering pipelines at the wellhead connection and remove any related surface equipment, and to remove certain components of gas transmission facilities from the ground.

During 2017 and 2016, our overall asset retirement obligation changed as follows (in thousands):

	2017			2016
Beginning balance	$	275,452		$	323,026
Accretion (1)	104,659			35,740
New obligations	28,447			7,995
Changes in estimates of existing obligations (2)	(38,470		)	(85,514		)
Property dispositions/obligations settled	(6,132		)	(5,795		)
Ending balance	$	363,956		$	275,452

(1) The increase in accretion for 2017 includes the cumulative effect of accretion adjustment associated with new AROs identified in our historical land agreements of $87 million that are not a component of new obligations.

(2) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal cost, discount rates, and the estimated remaining life of assets. The changes in estimates of existing obligations reflect a decrease of $38 million and $86 million for 2017 and 2016, respectively. The decrease in 2017 is primarily due to a decrease in current estimates for offshore removal costs. The decrease in 2016 is due primarily to revisions in the estimated remaining life of assets and the current estimate to the inflation rate.

We are entitled to collect in rates the amounts necessary to fund our ARO. All funds received for such retirements are deposited into an external trust account dedicated to funding our ARO. Under our current rate settlement our annual funding obligation is approximately $36.4 million, with installments to be deposited monthly (See Note 4).

9. REGULATORY ASSETS AND LIABILITIES

The regulatory assets and regulatory liabilities resulting from our application of the provisions of ASC Topic 980, Regulated Operations, included in the accompanying Consolidated Balance Sheet at December 31, 2017 and December 31, 2016 are as follows (in millions):

Regulatory Assets	2017		2016
Grossed-up deferred taxes on equity funds used during construction	$	37.9	$	73.2
Asset retirement obligations	168.7		117.2
Asset retirement costs - Eminence	49.5		53.9
Deferred taxes - asset	3.8		4.8
Deferred cash out	42.5		48.2
Deferred gas costs	6.0		—
Fuel cost	61.4		51.3
Other	3.7		2.5
Total Regulatory Assets	$	373.5	$	351.1

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Regulatory Liabilities	2017		2016
Negative salvage	$	409.7	$	357.1
Deferred taxes - liability	471.1		—
Sentinel meter station depreciation	6.3		6.2
Postretirement benefits other than pension	73.9		63.0
Electric power cost	13.3		6.3
Pension - deferred collections	32.5		21.3
Other	0.3		4.6
Total Regulatory Liabilities	$	1,007.1	$	458.5

The significant regulatory assets and liabilities include:

Grossed-up deferred taxes on equity funds used during construction: Regulatory asset balance established to offset the deferred tax for the equity component of the allowance for funds used during the construction of long-lived assets. All amounts were generated during the period that we were a taxable entity. Taxes on capitalized funds used during construction and the offsetting deferred income taxes are included in the rate base and are recovered over the depreciable lives of the long-lived asset to which they relate.

Asset retirement obligations: Regulatory asset balance established to offset depreciation of the ARO asset and changes in the ARO liability due to the passage of time. The regulatory asset is being recovered through our rates, and is being amortized to expense consistent with the amounts collected in rates (See Note 8).

Asset retirement costs - Eminence: Regulatory asset balance associated with the Eminence Storage Field retirement costs. The regulatory asset is being recovered through our rates, and is being amortized to expense consistent with the amounts collected in rates.

Deferred taxes - asset: Regulatory asset balance was established as a result of an increase to rate base deferred taxes due to an increase to the effective state income tax rate. The regulatory asset is being collected from rate payers over the remaining depreciable lives of the long-lived asset to which they relate.

Deferred cash out: This amount represents the deferral of gains or losses on the purchases and sales of gas imbalances with shippers. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual cash out filing periods.

Deferred gas costs: This amount arises from the movement of gas volumes between gas inventory accounts that have different valuations. These amounts are expected to be recovered/refunded in subsequent periods.

Fuel cost: This amount represents the difference between the gas retained from our customers and the gas consumed in operations. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual fuel tracker filing periods.

Negative salvage: Our rates include a component designed to recover certain future retirement costs for which we are not required to record an asset retirement obligation. We record a regulatory liability representing the cumulative residual amount of recoveries through rates, net of expenditures associated with these retirement costs.

Sentinel meter station depreciation: This amount reflects the incremental depreciation being recorded related to the meter station modifications made for three of the Sentinel shippers. These modifications will be recovered through a surcharge over a defined period of time as stated in the Sentinel FERC order. The incremental depreciation represents the difference between the FERC granted depreciation rate for such facilities in the last rate case as compared to the depreciation rates in the Sentinel order which are based on the contractual terms in the surcharge agreements. The incremental depreciation will be recorded through the end of the contractual term and then will be amortized.

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Postretirement benefits: We recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any difference between the annual actuarially determined cost and the amount recovered in rates is recorded as a regulatory asset or liability to be collected or refunded through future rate adjustments. These amounts are not included in the rate base (See Note 6).

Electric power cost: This amount represents the difference between the electric power costs recovered from our customers and the electric power costs incurred in operations. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual electric power tracker filing periods.

Pension - deferred collections: We recover the actuarially determined pension cash contributions through rates that are set through periodic general rate filings. Effective with the RP12-993 Settlement, any amounts of annual contributions that exceed an upper threshold or fall below a lower threshold are recorded as adjustments to income and collected or refunded through future rate adjustments (See Note 6).

Deferred taxes - liability: Regulatory liability balance was established as a result of a decrease to rate base deferred taxes due to a decrease to the effective federal income tax rate. The timing of the refund of the regulatory liability to rate payers will be subject to future discussions and negotiations with our customers in our next rate case.

10. OTHER

During 2017 and 2016, we capitalized $0.2 million and $1.4 million, respectively, of project feasibility costs, which had been expensed in prior periods in Other expense, net, upon determining that the project was probable of development.

The Advances for construction costs on the Consolidated Balance Sheet are associated with advances received from third parties related to construction costs on the Atlantic Sunrise and Dalton projects. This balance increases as we receive additional advances. After construction of the respective projects are completed, the related liabilities will be reclassified to Long-Term Debt and reduced by payments we make to the third parties under terms of the applicable lease agreements. In the third quarter of 2017, the advances received from a third party related to construction costs on the Dalton lateral was reclassified to Long-Term Debt on our Consolidated Balance Sheet.

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TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC

QUARTERLY FINANCIAL DATA (UNAUDITED)

Summarized quarterly financial data are as follows (in thousands):

2017	First			Second			Third			Fourth (1)
Operating revenues	$	413,716		$	432,502		$	452,052		$	476,735
Operating expenses	246,539			274,719			300,436			799,397
Operating income (loss)	167,177			157,783			151,616			(322,662		)
Interest expense	37,257			37,236			41,304			43,077
Other (income) and deductions, net	(24,936		)	(31,121		)	(24,020		)	19,389
Net income (loss)	154,856			151,668			134,332			(385,128		)
Equity interest in unrealized gain (loss) on interest rate hedge	35			1			72			219
Comprehensive income (loss)	$	154,891		$	151,669		$	134,404		$	(384,909	)

2016	First (2)			Second			Third			Fourth
Operating revenues	$	395,866		$	393,017		$	412,849		$	414,403
Operating expenses	242,691			245,375			264,686			264,295
Operating income	153,175			147,642			148,163			150,108
Interest expense	38,822			37,817			37,318			37,337
Other (income) and deductions, net	(10,365		)	(18,015		)	(21,068		)	(26,133		)
Net income	124,718			127,840			131,913			138,904
Equity interest in unrealized gain (loss) on interest rate hedge	(234		)	(50		)	156			169
Comprehensive income	$	124,484		$	127,790		$	132,069		$	139,073

(1) Includes $471.1 million increase to operating expenses for a regulatory charge resulting from Tax Reform. Includes $12.2 million increase to operating expenses for the portion of Williams' pension settlement costs charged to us. Includes $32.7 million unfavorable change to other (income) and deductions, net for regulatory assets associated with the effects of deferred taxes on equity funds used during construction as a result of Tax Reform. Includes $10.3 million unfavorable change to other (income) and deductions, net for regulatory charge resulting from Tax Reform for our equity investments.

(2) Includes $15.0 million decrease to operating revenues to establish an accrual for Washington Storage Service potential refunds. Includes $6.3 million increase to operating expenses for severance related costs. Includes $2.9 million increase to interest expense related to interest on refunds for Washington Storage Services.

54

Item 9.Changes In and Disagreements With Accountants on Accounting and Financial Disclosure

None.

Item 9A. Controls and Procedures

Disclosure Controls and Procedures

Our management, including our Senior Vice President and our Vice President, Controller and Chief Accounting Officer, does not expect that our disclosure controls and procedures (as defined in Rules 13a—15(e) and 15d—15(e) of the Securities Exchange Act) (Disclosure Controls) will prevent all errors and all fraud. A control system, no matter how well conceived and operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Further, the design of a control system must reflect the fact that there are resource constraints, and the benefits of controls must be considered relative to their costs. Because of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, within the company have been detected. These inherent limitations include the realities that judgments in decision-making can be faulty, and that breakdowns can occur because of simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons, by collusion of two or more people, or by management override of the control. The design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions. Because of the inherent limitations in a cost-effective control system, misstatements due to error or fraud may occur and not be detected. We monitor our Disclosure Controls and make modifications as necessary; our intent in this regard is that the Disclosure Controls will be modified as systems change and conditions warrant.

Evaluation of Disclosure Controls and Procedures

An evaluation of the effectiveness of the design and operation of our Disclosure Controls was performed as of the end of the period covered by this report. This evaluation was performed under the supervision and with the participation of our management, including our Senior Vice President and our Vice President, Controller and Chief Accounting Officer. Based upon that evaluation, our Senior Vice President and our Vice President, Controller and Chief Accounting Officer concluded that these Disclosure Controls are effective at a reasonable assurance level.

Changes in Internal Control over Financial Reporting

There have been no changes during the fourth quarter of 2017 that have materially affected, or are reasonably likely to materially affect, our Internal Control over Financial Reporting.

Management’s Annual Report on Internal Control over Financial Reporting

Management is responsible for establishing and maintaining adequate internal control over financial reporting (as defined in Rules 13a – 15(f) and 15d – 15(f) under the Securities Exchange Act of 1934). Our internal control over financial reporting is designed to provide reasonable assurance to our management regarding the preparation and fair presentation of financial statements in accordance with accounting principles generally accepted in the United States. Our internal control over financial reporting includes those policies and procedures that (i) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of our assets; (ii) provide reasonable assurance that transactions are recorded as to permit preparation of financial statements in accordance with generally accepted accounting principles, and that our receipts and expenditures are being made only in accordance with authorization of our management; and (iii) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of our assets that could have a material effect on our financial statements.

All internal control systems, no matter how well designed, have inherent limitations including the possibility of human error and the circumvention or overriding of controls. Therefore, even those systems determined to be effective can provide only reasonable assurance with respect to financial statement preparation and presentation.

55

Under the supervision and with the participation of our management, including our Senior Vice President and our Vice President, Controller and Chief Accounting Officer, we assessed the effectiveness of our internal control over financial reporting as of December 31, 2017, based on the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission (COSO) in Internal Control — Integrated Framework (2013). Based on our assessment, we concluded that, as of December 31, 2017, our internal control over financial reporting was effective.

This annual report does not include a report of the company’s registered public accounting firm regarding internal control over financial reporting. A report by the company’s registered public accounting firm is not required pursuant to rules of the Securities and Exchange Commission that permit us to provide only management’s report in this annual report.

Item 9B.Other information

None.

PART III

Since we meet the conditions set forth in General Instruction (I)(1)(a) and (b) of Form 10-K, the information required by Items 10, 11, 12, and 13, is omitted.

Items 14.Principal Accounting Fees and Services

Fees for professional services provided by our independent registered public accounting firm in each of the last two fiscal years in each of the following categories are (in thousands):

	2017		2016
Audit fees	$	1,300	$	1,314
Audit-related fees	—		—
Tax fees	—		—
All other fees	—		—
Total fees	$	1,300	$	1,314

Fees for audit services include fees associated with the annual audit, the reviews for our quarterly reports on Form 10-Q, the reviews for other SEC and FERC filings, and accounting consultation.

As a wholly owned subsidiary of WPZ, we do not have a separate audit committee. The policies and procedures for pre-approving audit and non-audit services of the Audit Committee of the Board of Directors of WPZ’s general partner have been set forth in WPZ’s 2017 annual report on Form 10-K, which is available on the SEC’s website at http://www.sec.gov and on http://investor.williams.com.

56

PART IV

Item 15. Exhibits and Financial Statement Schedules

	Page Reference to 2017 10-K
A. 1 and 2. Transcontinental Gas Pipe Line Company, LLC financials
Index
Covered by Report of Independent Registered Public Accounting Firm:
Consolidated Statement of Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015	30
Consolidated Balance Sheet as of December 31, 2017 and 2016	31
Consolidated Statement of Member’s Equity for the Years Ended December 31, 2017, 2016 and 2015	33
Consolidated Statement of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015	34
Notes to Consolidated Financial Statements	36
Not covered by Report of Independent Registered Public Accounting Firm:
Quarterly Financial Data (Unaudited)	54
The following schedules are omitted because of the absence of the conditions under which they are required: I, II, III, IV, and V.

57

3. Exhibits:

Exhibit Number	Description
2	Certificate of Conversion dated December 22, 2008 and effective December 31, 2008 (filed on February 24, 2011 as Exhibit 2.1 to our annual report on Form 10-K (File No. 001-07584) and incorporated herein by reference).
3.1	Certificate of Formation executed as of December 22, 2008 and effective December 31, 2008 (filed on February 24, 2011 as Exhibit 3.1 to our annual report on Form 10-K (File No. 001-07584) and incorporated herein by reference).
3.2	Amended and Restated Operating Agreement of Transcontinental Gas Pipe Line Company, LLC dated February 17, 2010 (filed on October 28, 2010 as Exhibit 3.2 to our quarterly report on Form 10-Q (File No. 001-07584) and incorporated herein by reference).
4.1	Senior Indenture dated July 15, 1996 between Transcontinental Gas Pipe Line Corporation and Citibank, N.A., as Trustee (filed on April 2, 1996 as Exhibit 4.1 to our registration statement Form S-3 (File No. 333-02155) and incorporated herein by reference).
4.2	Indenture, dated as of May 22, 2008 between Transcontinental Gas Pipe Line Corporation and The Bank of New York Trust Company, N.A., as Trustee (filed on May 23, 2008 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07584) and incorporated herein by reference).
4.3	Indenture, dated as of August 12, 2011 between Transcontinental Gas Pipe Line Company, LLC and The Bank of New York Mellon Trust Company, N.A., as Trustee (filed on August 12, 2011 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07584) and incorporated herein by reference).
4.4	Indenture, dated as of July 13, 2012, between Transcontinental Gas Pipe Line Company, LLC and The Bank of New York Mellon Trust Company, N.A., as Trustee (filed on July 16, 2012 as Exhibit 4.1 to our current report Form 8-K (File No. 001-07584) and incorporated herein by reference).
4.5	Indenture, dated as of January 22, 2016, between Transcontinental Gas Pipe Line Company, LLC and The Bank of New York Mellon Trust Company, N.A., as trustee (filed on January 22, 2016 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07584) and incorporated herein by reference).
10.1	Administrative Services Agreement, dated as of February 17, 2010, by and between Transco Pipeline Services LLC and Transcontinental Gas Pipe Line Company, LLC (filed on February 22, 2010 as Exhibit 10.3 to Williams Partners L.P.’s, Form 8-K (File No. 001-32599) and incorporated herein by reference).
10.2	Assignment Agreement dated February 13, 2013 by and between Transco Pipeline Services LLC and Williams WPC-I, LLC, effective January 1, 2013 (filed on February 27, 2013 as Exhibit 10.2 to our annual report on Form 10-K (File No. 001-07584) and incorporated herein by reference).
10.3	Second Amended and Restated Credit Agreement dated as of February 2, 2015, between Williams Partners L.P. (formerly known as Access Midstream Partners, L.P.), Northwest Pipeline LLC, Transcontinental Gas Pipeline Company, LLC, as co-borrowers, the lenders named therein, and Citibank, N.A. as Administrative Agent (filed on February 3, 2015 as Exhibit 10.1 to Williams Partners L.P.’s current report on Form 8-K (File No. 001-34831) and incorporated herein by reference).
10.4	Amendment No. 1 to Second Amended & Restated Credit Agreement dated December 18, 2015, between Williams Partners L.P., Northwest Pipeline LLC, Transcontinental Gas Pipe Line Company, LLC, as co-borrowers, the lenders named therein, and Citibank, N.A. as Administrative Agent (filed on December 23, 2015 as Exhibit 10.1 to our current Form 8-K (File No. 001-07584) and incorporated herein by reference).
10.5	Amendment No. 2 and Extension Agreement, dated as of November 17, 2017, by and among Williams Partners L.P., Northwest Pipeline LLC, Transcontinental Gas Pipe Line Company, LLC, the lenders party thereto and Citibank, N.A. (filed on November 22, 2017 as Exhibit 10.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
31.1*	Certification of Principal Executive Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended, and Item 601(b)(31) of Regulation S-K, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.

58

31.2*	Certification of Principal Financial Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended, and Item 601(b)(31) of Regulation S-K, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
32 **	Certification of Principal Executive Officer and Principal Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.

101.INS* 101.I SCH * 101.CAL* 101.DEF* 101.LAB*	XBRL Instance Document. XBRL Taxonomy Extension Schema. XBRL Taxonomy Extension Calculation Linkbase. XBRL Taxonomy Extension Definition Linkbase. XBRL Taxonomy Extension Label Linkbase.
101.PRE*	XBRL Taxonomy Extension Presentation Linkbase.

*     Filed herewith.

**    Furnished herewith.

Item 16.Form 10-K Summary

Not applicable.

59

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC (Registrant)
By:	/s/ Ted T. Timmermans
	Ted T. Timmermans
	Vice President, Controller and Chief Accounting Officer (Principal Accounting Officer)

Date: February 22, 2018

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated:

Signature	Title
/s/ Frank J. Ferazzi	Management Committee Member and Senior Vice President (Principal Executive Officer)
Frank J. Ferazzi
/s/ Ted T. Timmermans	Vice President, Controller and Chief Accounting Officer (Principal Financial and Accounting Officer)
Ted T. Timmermans

Date: February 22, 2018

EX-31.1

Exhibit 31.1

SECTION 302 CERTIFICATION

I, Frank J. Ferazzi, certify that:

1. I have reviewed this annual report on Form 10-K of Transcontinental Gas Pipe Line Company, LLC;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 22, 2018

By:	/s/ Frank J. Ferazzi
	Frank J. Ferazzi
	Senior Vice President
	(Principal Executive Officer)

EX-31.2

Exhibit 31.2

SECTION 302 CERTIFICATION

I, Ted T. Timmermans, certify that:

1. I have reviewed this annual report on Form 10-K of Transcontinental Gas Pipe Line Company, LLC;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 22, 2018

By:	/s/ Ted T. Timmermans
	Ted T. Timmermans
	Vice President, Controller and Chief Accounting Officer
	(Principal Financial Officer)

EX-32

Exhibit 32

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of Transcontinental Gas Pipe Line Company, LLC (the “Company”) on Form 10-K for the period ending December 31, 2017 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), each of the undersigned hereby certifies, in his capacity as an officer of the Company, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that to his knowledge:

(1) The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Frank J. Ferazzi

Frank J. Ferazzi

Senior Vice President

February 22, 2018

/s/ Ted T. Timmermans

Ted T. Timmermans

Vice President, Controller and Chief Accounting Officer

February 22, 2018

A signed original of this written statement required by Section 906 has been provided to, and will be retained by, the Company and furnished to the Securities and Exchange Commission or its staff upon request.

The foregoing certification is being furnished to the Securities and Exchange Commission as an exhibit to the Report and shall not be considered filed as part of the Report.

XML

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 22, 2018
Entity Information [Line Items]
Entity Registrant Name	Transcontinental Gas Pipe Line Company, LLC
Entity Central Index Key	0000099250
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		0
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 0

XML

Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues:
Natural gas sales	$ 99,100	$ 86,720	$ 125,774
Natural gas transportation	1,531,778	1,397,341	1,318,656
Natural gas storage	137,348	122,555	137,983
Other	6,779	9,519	10,106
Total operating revenues	1,775,005	1,616,135	1,592,519
Operating Costs and Expenses:
Cost of natural gas sales	99,100	86,720	125,774
Cost of natural gas transportation	19,589	19,689	26,501
Operation and maintenance	401,871	316,989	288,386
Administrative and general	182,121	168,759	179,489
Depreciation and amortization	318,058	307,707	277,850
Taxes - other than income taxes	65,612	60,119	49,567
Regulatory charge resulting from Tax Reform (Note 1)	471,096	0	0
Other expense, net	63,644	57,064	57,800
Total operating costs and expenses	1,621,091	1,017,047	1,005,367
Operating Income	153,914	599,088	587,152
Other (Income) and Other Expenses:
Interest expense - affiliate	60	60	64
Interest expense - other	158,814	151,234	82,774
Interest income - affiliate	(3,507)	(2,201)	(28)
Interest income - other	(2,782)	(2,185)	(1,933)
Allowance for equity and borrowed funds used during construction (AFUDC)	(92,013)	(68,964)	(63,072)
Equity in (earnings) loss of unconsolidated affiliates	6,188	(5,914)	(5,593)
Miscellaneous other (income) expenses, net	31,426	3,683	(517)
Total other (income) and other expenses	98,186	75,713	11,695
Net Income	55,728	523,375	575,457
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes $103, $167, and $316 for the years ended December 31, 2017, 2016, and 2015, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	327	41	84
Comprehensive Income	$ 56,055	$ 523,416	$ 575,541

XML

Consolidated Statement of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Accumulated other comprehensive income reclassification for realized losses on interest rate hedges	$ 103	$ 167	$ 316

XML

Consolidated Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash	$ 0	$ 0
Receivables:
Trade	167,928	141,726
Affiliates	1,109	489
Advances to affiliate	395,247	811,693
Other	2,494	2,589
Transportation and exchange gas receivables	3,205	1,827
Inventories:
Gas in storage, at original cost	790	786
Gas available for customer nomination, at average cost	1,850	17,233
Materials and supplies, at lower of average cost or market	37,387	37,190
Regulatory assets	97,149	87,059
Other	12,508	13,305
Total current assets	719,667	1,113,897
Investments, at cost plus equity in undistributed earnings	28,505	42,403
Property, Plant and Equipment:
Natural gas transmission plant	13,771,183	11,996,454
Less-Accumulated depreciation and amortization	3,859,520	3,687,473
Total property, plant and equipment, net	9,911,663	8,308,981
Other Assets:
Regulatory assets	276,315	264,001
Other	141,786	102,198
Total other assets	418,101	366,199
Total assets	11,077,936	9,831,480
Payables:
Trade	444,021	211,829
Affiliates	43,420	29,455
Cash overdrafts	25,132	40,043
Transportation and exchange gas payables	2,121	1,571
Accrued liabilities:
Property and other taxes	12,843	13,594
Interest	49,900	49,900
Regulatory liabilities	16,350	9,120
Customer deposits	15,754	47,049
Customer advances	44,689	34,923
Asset retirement obligations	13,676	26,934
Other	20,390	16,177
Long-term debt due within one year	251,430	0
Total current liabilities	939,726	480,595
Long-Term Debt	2,191,576	2,210,754
Other Long-Term Liabilities:
Asset retirement obligations	350,280	248,518
Regulatory liabilities	990,702	449,391
Advances for construction costs	426,771	283,028
Transportation prepayments	10,871	11,837
Deferred revenue	225,858	0
Other	4,828	6,088
Total other long-term liabilities	2,009,310	998,862
Contingent Liabilities and Commitments (Note 2)
Member's Equity:
Member's capital	4,088,499	3,678,499
Retained earnings	1,848,488	2,462,760
Accumulated other comprehensive income	337	10
Total member's equity	5,937,324	6,141,269
Total liabilities and member's equity	$ 11,077,936	$ 9,831,480

XML

Consolidated Balance Sheet Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for receivables	$ 0	$ 0

XML

Consolidated Statement of Member's Equity Consolidated Statement of Member's Equity - USD ($) $ in Thousands	Total	Member's Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period at Dec. 31, 2014		$ 2,524,499	$ 2,339,928	$ (115)
Cash contributions from parent	$ 652,000	652,000
Net income	575,457		575,457
Cash distributions to parent	(536,000)		(536,000)
Equity interest in unrealized gain on interest rate hedge	84			84
Noncash distribution to Parent			0
Balance at end of period at Dec. 31, 2015	5,555,853	3,176,499	2,379,385	(31)
Cash contributions from parent	502,000	502,000
Net income	523,375		523,375
Cash distributions to parent	(440,000)		(440,000)
Equity interest in unrealized gain on interest rate hedge	41			41
Noncash distribution to Parent			0
Balance at end of period at Dec. 31, 2016	6,141,269	3,678,499	2,462,760	10
Cash contributions from parent	410,000	410,000
Net income	55,728		55,728
Cash distributions to parent	(430,000)		(430,000)
Equity interest in unrealized gain on interest rate hedge	327			327
Noncash distribution to Parent			240,000
Balance at end of period at Dec. 31, 2017	$ 5,937,324	$ 4,088,499	$ 1,848,488	$ 337

XML

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 55,728	$ 523,375	$ 575,457
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	318,058	307,707	277,850
Allowance for equity funds used during construction (equity AFUDC)	(69,653)	(56,468)	(48,435)
Regulatory charge resulting from Tax Reform (Note 1)	471,096	0	0
Changes in operating assets and liabilities:
Receivables - affiliates	(620)	595	(430)
Receivables - trade and other	(26,107)	5,941	(19,521)
Transportation and exchange gas receivable	(1,378)	600	1,058
Regulatory assets - current	(10,090)	(7,484)	(1,765)
Regulatory assets - non-current	(10,761)	(271)	(24,650)
Inventories	15,182	1,632	9,858
Payables - affiliates	12,514	(10,909)	2,676
Payables - trade	(9,823)	29,375	(2,077)
Accrued liabilities	(29,651)	74,759	(10,015)
Asset retirement obligations - non-current	103,105	31,114	19,022
Asset retirement obligation - removal costs	(4,578)	(4,911)	(3,097)
Deferred Revenue	(4,542)	0	0
Other, net	14,415	32,030	45,007
Net cash provided by operating activities	822,895	927,085	820,938
Cash flows from financing activities:
Proceeds from long-term debt	0	998,250	0
Retirement of long-term debt	0	200,000	0
Payments on other financing obligations	(486)	0	0
Payments of debt issuance costs	13	8,381	0
Cash distributions to parent	(430,000)	(440,000)	(536,000)
Cash contributions from parent	410,000	502,000	652,000
Net cash provided by (used in) financing activities	(20,499)	851,869	116,000
Cash flows from investing activities:
Property, plant and equipment additions, net of equity AFUDC	(1,576,611)	(1,213,969)	(1,270,860)
Contributions and Advances for Construction Costs	425,397	216,447	85,901
Disposal of property, plant and equipment, net	(49,090)	(12,529)	(12,358)
Advances to affiliate, net	416,446	(747,085)	242,302
Return of capital from unconsolidated affiliates	3,926	2,767	2,015
Purchase of ARO Trust investments	(57,099)	(70,901)	(64,087)
Proceeds from sale of ARO Trust investments	31,435	44,195	43,284
Proceeds from insurance	3,200	2,121	35,132
Other, net	0	0	1,560
Net cash used in investing activities	(802,396)	(1,778,954)	(937,111)
Increase (decrease) in cash	0	0	(173)
Cash at beginning of period	0	0	173
Cash at end of period	0	0	0
Increase to property, plant and equipment, net of equity AFUDC	(1,784,254)	(1,200,696)	(1,222,292)
Changes in related accounts payable and accrued liabilities	207,643	(13,273)	(48,568)
Property, plant and equipment additions, net of equity AFUDC	(1,576,611)	(1,213,969)	(1,270,860)
Supplemental Cash Flow Elements [Abstract]
Interest (exclusive of amount capitalized)	136,439	103,391	66,489
Income taxes	$ 2,089	$ 828	$ 1,161

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Summary of Significant Accounting Policies (Notes)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Significant Accounting Policies

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Corporate Structure and Control

In this report, Transco (which includes Transcontinental Gas Pipe Line Company, LLC and, unless the context otherwise requires, all of our majority-owned subsidiaries) is at times referred to in the first person as “we,” “us” or “our.”

Transco is indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which is consolidated by The Williams Companies, Inc. (Williams). In January 2017, Williams permanently waived the WPZ general partner's incentive distribution rights, converted its 2 percent general partner interest in WPZ to a non-economic interest and purchased additional WPZ common units. At December 31, 2017, Williams owns a 74 percent limited partner interest in WPZ.

Transco is a single member limited liability company, and as such, single member losses are limited to the amount of its investment.

Related Party Transaction

A former member of Williams' Board of Directors, who was elected in 2013 and resigned during 2016, is also the current chairman, president, and chief executive officer of Public Service Enterprise Group, an energy services company that is a customers of ours. This board member does not have any material interest in any transactions between the energy services company and us and he had no role in any such transactions.

Nature of Operations

We are an interstate natural gas transmission company that owns a natural gas pipeline system extending from Texas, Louisiana, Mississippi and the Gulf of Mexico through Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, Pennsylvania and New Jersey to the New York City metropolitan area. The system serves customers in Texas and the 12 southeast and Atlantic seaboard states mentioned above, including major metropolitan areas in Georgia, Washington D.C., Maryland, North Carolina, New York, New Jersey and Pennsylvania.

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). The Accounting Standards Codification (ASC) Regulated Operations (Topic 980), provides that rate-regulated public utilities account for and report regulatory assets and liabilities consistent with the economic effect of the way in which regulators establish rates if the rates established are designed to recover the costs of providing the regulated service and if the competitive environment makes it probable that such rates can be charged and collected. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, employee related benefits, environmental costs, negative salvage, asset retirement obligations (ARO), and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980 and, accordingly, the accompanying consolidated financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

In December 2017, the Tax Cuts and Jobs Act was enacted, which, among other things, reduced the federal corporate income tax rate from 35 percent to 21 percent (Tax Reform). In accordance with ASC 980-740-25-2, we have recognized a regulatory liability to reflect the probable return to certain customers through future rates of the future decrease in income taxes payable associated with Tax Reform. In determining the estimated liability that we currently believe is probable of return to certain customers through future rates, we considered the mix of services provided by us, taking into consideration that certain of these services are provided under contractually based rates, in lieu of recourse-based rates, that are designed to recover the cost of providing those services, with no expected future rate adjustment for the term of those contracts. The liability was recorded in December 2017 through a regulatory charge to operating income of $471.1 million. The timing and actual amount of such return will be subject to future negotiations regarding this matter and many other elements of cost-of-service rate proceedings, including other costs of providing service.

Certain of our equity-method investees recorded similar regulatory liabilities, for which our Equity in (earnings) loss of unconsolidated affiliates on our Consolidated Statement of Comprehensive Income has been reduced by $10.3 million related to our proportionate share of the associated regulatory charges.

Our regulatory asset associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $32.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net on our Consolidated Statement of Comprehensive Income.

Basis of Presentation

Williams’ acquisition of Transco Energy Company and its subsidiaries, including us, in 1995 was accounted for using the purchase method of accounting. Accordingly, an allocation of the purchase price was assigned to our assets and liabilities based on their estimated fair values. The purchase price allocation to us primarily consisted of a $1.5 billion allocation to property, plant and equipment and adjustments to deferred taxes based upon the book basis of the net assets recorded as a result of the acquisition. The amount allocated to property, plant and equipment is being depreciated on a straight-line basis over 40 years, the estimated useful lives of these assets at the date of acquisition, at approximately $35 million per year. At December 31, 2017, the remaining property, plant and equipment allocation was approximately $0.6 billion. Current FERC policy does not permit us to recover through rates amounts in excess of original cost.

Principles of Consolidation

The consolidated financial statements include our accounts and the accounts of the subsidiaries we control. Companies in which we and our subsidiaries own 20 percent to 50 percent of the voting common stock or otherwise exercise significant influence over operating and financial policies of the company are accounted for under the equity method. The equity method investments as of December 31, 2017 and December 31, 2016 consist of Cardinal Pipeline Company, LLC (Cardinal) with ownership interest of approximately 45 percent and Pine Needle LNG Company, LLC (Pine Needle) with ownership interest of 35 percent. We received distributions associated with our equity method investments totaling $8.0 million, $8.6 million, and $7.6 million in 2017, 2016 and 2015, respectively. Included in the distributions are $3.9 million, $2.8 million and $2.0 million return of capital in 2017, 2016 and 2015, respectively.

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Estimates and assumptions which, in the opinion of management, are significant to the underlying amounts included in the financial statements and for which it would be reasonably possible that future events or information could change those estimates include: 1) revenues subject to refund; 2) litigation-related contingencies; 3) environmental remediation obligations; 4) impairment assessments of long-lived assets; 5) depreciation; 6) asset retirement obligations; and 7) regulatory deferred taxes.

Revenue Recognition

Revenues for transportation of gas under long-term firm agreements are recognized considering separately the reservation and commodity charges. Reservation revenues are recognized monthly over the term of the agreement regardless of the volume of natural gas transported. Commodity revenues from both firm and interruptible transportation are recognized in the period transportation services are provided based on volumes of natural gas physically delivered at the agreed upon delivery point. Revenues for the storage of gas under firm agreements are recognized considering separately the reservation, capacity, and injection and withdrawal charges. Reservation and capacity revenues are recognized monthly over the term of the agreement regardless of the volume of storage service actually utilized. Injection and withdrawal revenues are recognized in the period when volumes of natural gas are physically injected into or withdrawn from storage.

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. The resulting imbalances are primarily settled through the purchase and sale of gas with our customers under terms provided in our FERC tariff. Revenue is recognized from the sale of gas upon settlement of the transportation and exchange imbalances (See Gas Imbalances in this Note).

As a result of the ratemaking process, certain revenues collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel and other risks.

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that any expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

Property, Plant and Equipment

Property, plant and equipment is recorded at cost. The carrying values of these assets are also based on estimates, assumptions and judgments relative to capitalized costs, useful lives and salvage values. These estimates, assumptions and judgments reflect FERC regulations, as well as historical experience and expectations regarding future industry conditions and operations. The FERC identifies installation, construction and replacement costs that are to be capitalized. All other costs are expensed as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are credited or charged to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission facilities, production and gathering facilities and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC. Depreciation rates used for major regulated gas plant facilities at December 31, 2017, 2016 and 2015 are as follows:

Category of Property	2017-2015
Gathering facilities	1.35% - 2.50%
Storage facilities	2.10% -  2.25%
Onshore transmission facilities	2.61%  -  5.00%
Offshore transmission facilities	1.20%  -  1.20%

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurements of AROs include, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as a market-risk premium. The ARO asset is depreciated in a manner consistent with the expected timing of the future abandonment of the underlying physical assets. We measure changes in the liability due to passage of time by applying an interest method of allocation. The depreciation of the ARO asset and accretion of the ARO liability are recognized as an increase to a regulatory asset, as management expects to recover such amounts in future rates. The regulatory asset is amortized commensurate with our collection of these costs in rates.

Impairment of Long-lived Assets

We evaluate the long lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. When an indicator of a potential impairment has occurred we compare our management’s estimate of undiscounted future cash flows attributable to the assets to the carrying value of the assets to determine whether an impairment has occurred. We apply a probability-weighted approach to consider the likelihood of different cash flow assumptions and possible outcomes including selling in the near term or holding for the remaining estimated useful life. If an impairment of the carrying value has occurred, we determine the amount of the impairment recognized in the financial statements by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

For assets identified to be disposed of in the future and considered held for sale in accordance with the ASC Property, Plant, and Equipment (Topic 360), we compare the carrying value to the estimated fair value less the cost to sell to determine if recognition of an impairment is required. Until the assets are disposed of, the estimated fair value, which includes estimated cash flows from operations until the assumed date of sale, is recalculated when related events or circumstances change.

Judgments and assumptions are inherent in our management’s estimate of undiscounted future cash flows used to determine recoverability of an asset and the estimate of an asset’s fair value used to calculate the amount of impairment to recognize.

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and are included as a cost of property, plant and equipment because it constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $22.3 million, $12.5 million and $14.6 million, for 2017, 2016 and 2015, respectively. The allowance for equity funds was $69.7 million, $56.5 million, and $48.4 million, for 2017, 2016 and 2015, respectively.

Income Taxes

We generally are not a taxable entity for federal or state and local income tax purposes. The tax on net income is generally borne by unitholders of our ultimate parent, WPZ. Net income for financial statement purposes may differ significantly from taxable income of WPZ’s unitholders as a result of differences between the tax basis and financial reporting basis of assets and liabilities and the taxable income allocation requirements under the WPZ partnership agreement. The aggregated difference in the basis of our assets for financial and tax reporting purposes cannot be readily determined because information regarding each of WPZ’s unitholder’s tax attributes in WPZ is not available to us.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts receivable are stated at the historical carrying amount net of reserves or write-offs. Our credit risk exposure in the event of nonperformance by the other parties is limited to the face value of the receivables. We perform ongoing credit evaluations of our customers’ financial condition and require collateral from our customers, if necessary. Due to our customer base, we have not historically experienced recurring credit losses in connection with our receivables. Receivables determined to be uncollectible are reserved or written off in the period of determination.

Gas Imbalances

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. Additionally, we transport gas on various pipeline systems which may deliver different quantities of gas on behalf of us than the quantities of gas received from us. These transactions result in gas transportation and exchange imbalance receivables and payables which are recovered or repaid in cash or through the receipt or delivery of gas in the future and are recorded in the accompanying Consolidated Balance Sheet. Settlement of imbalances requires agreement between the pipelines and shippers as to allocations of volumes to specific transportation contracts and timing of delivery of gas based on operational conditions. Our tariff includes a method whereby most transportation imbalances are settled on a monthly basis. Each month a portion of the imbalances are not identified to specific parties and remain unsettled. These are generally identified to specific parties and settled in subsequent periods. We believe that amounts that remain unidentified to specific parties and unsettled at year end are valid balances that will be settled with no material adverse effect upon our financial position, results of operations or cash flows. Management has implemented a policy of continuing to carry any unidentified transportation and exchange imbalances on the books for a three-year period. At the end of the three year period a final assessment will be made of their continued validity. Absent a valid reason for maintaining the imbalance, any remaining balance will be recognized in income. Certain imbalances are being recovered or repaid in cash or through the receipt or delivery of gas upon agreement of the parties as to the allocation of the gas volumes, and as permitted by pipeline operating conditions. These imbalances have been classified as current assets and current liabilities at December 31, 2017 and 2016. We utilize the average cost method of accounting for gas imbalances.

Deferred Cash Out

Most transportation imbalances are settled in cash on a monthly basis (cash out). We are required by our tariff to refund revenues received from the cash out of transportation imbalances in excess of costs incurred during the annual August through July reporting period. Revenues received in excess of costs incurred are deferred until refunded in accordance with the tariff.

Gas Inventory

We utilize the last-in, first-out (LIFO) method of accounting for inventory gas in storage. At December 31, 2017 and 2016, Gas in Storage, at LIFO, was zero. The basis for determining current cost at the end of each year is the December monthly average gas price delivered to pipelines in Texas and Louisiana. We utilize the average cost method of accounting for gas available for customer nomination. Liquefied natural gas in storage is valued at original cost.

Materials and Supplies Inventory

All inventories are stated at lower of average cost or net realizable value. We perform an annual review of Materials and Supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2017 and 2016.

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans. (See Note 6.) Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us and thus paid by us, is based on our share of net periodic benefit cost.

Cash Flows from Operating Activities and Cash Equivalents

We use the indirect method to report cash flows from operating activities, which requires adjustments to net income to reconcile to net cash flows provided by operating activities. We include short-term, highly-liquid investments that have an original maturity of three months or less as cash equivalents.

Accounting Standards Issued But Not Yet Adopted

In August 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-15 “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15). ASU 2016-15 provides specific guidance on eight cash flow classification issues, including debt prepayment or debt extinguishment costs and distributions received from equity method investees, to reduce diversity in practice. ASU 2016-15 is effective for interim and annual periods beginning after December 15, 2017. Early adoption is permitted. ASU 2016-15 requires a retrospective transition. We do not expect ASU 2016-15 to have a material impact on our consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13 “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 changes the impairment model for most financial assets and certain other instruments. For trade and other receivables, held-to-maturity debt securities, loans, and other instruments, entities will be required to use a new forward-looking “expected loss” model that generally will result in the earlier recognition of allowances for losses. The guidance also requires increased disclosures. ASU 2016-13 is effective for interim and annual periods beginning after December 15, 2019. Early adoption is permitted. ASU 2016-13 requires varying transition methods for the different categories of amendments. We do not expect ASU 2016-13 to have a significant impact on our consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02 “Leases (Topic 842)” (ASU 2016-02). ASU 2016-02 establishes a comprehensive new lease accounting model. ASU 2016-02 modifies the definition of a lease, requires a dual approach to lease classification similar to current lease accounting, and causes lessees to recognize leases on the balance sheet as a lease liability measured as the present value of the future lease payments with a corresponding right-of-use asset, with an exception for leases with a term of one year or less. Additional disclosures will also be required regarding the amount, timing, and uncertainty of cash flows arising from leases. In January 2018, the FASB issued ASU 2018-01 “Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842” (ASU 2018-01). Per ASU 2018-01, land easements and rights-of-way are required to be assessed under ASU 2016-02 to determine whether the arrangements are or contain a lease and permits an entity to elect a transition practical expedient to not apply ASU 2016-02 to land easements that exist or expired before the effective date of ASU 2016-02 and that were not previously assessed under the previous lease guidance in ASC Topic 840 “Leases”. ASU 2016-02 is effective for interim and annual periods beginning after December 15, 2018. Early adoption is permitted. ASU 2016-02 currently requires a modified retrospective transition for financing or operating leases existing at or entered into after the beginning of the earliest comparative period presented in the financial statements.

In January 2018, the FASB proposed an accounting standard update titled “Leases (Topic 842): Targeted Improvements”, which is an update to ASU 2016-02 allowing entities an additional transition method to the existing requirements whereby an entity could adopt the provisions of ASU 2016-02 by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption without adjustment to the financial statements for periods prior to adoption. We expect to adopt ASU 2016-02 effective January 1, 2019. We are in the process of reviewing contracts to identify leases based on the modified definition of a lease, implementing a financial lease accounting system, and evaluating internal control changes to support management in the accounting for and disclosure of leasing activities. While we are still in the process of completing our implementation evaluation of ASU 2016-02, we currently believe the most significant changes relate to the recognition of a lease liability and offsetting right-of-use asset in our Consolidated Balance Sheet for operating leases. We are also evaluating ASU 2016-02's currently available and proposed practical expedients on adoption.

In May 2014, the FASB issued ASU 2014-09 establishing ASC Topic 606, “Revenue from Contracts with Customers” (ASC 606). ASC 606 establishes a comprehensive new revenue recognition model designed to depict the transfer of goods or services to a customer in an amount that reflects the consideration the entity expects to be entitled to receive in exchange for those goods or services and requires significantly enhanced revenue disclosures. In August 2015, the FASB issued ASU 2015-14 “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date” (ASU 2015-14). Per ASU 2015-14, the standard is effective for interim and annual reporting periods beginning after December 15, 2017. ASC 606 allows either full retrospective or modified retrospective transition and early adoption is permitted for annual periods beginning after December 15, 2016. We are adopting ASC 606 utilizing the modified retrospective transition approach, effective January 1, 2018. We do not anticipate any cumulative effect adjustment to retained earnings upon initially applying ASC 606 for periods prior to January 1, 2018.

We are in the final stages of evaluating the impact ASC 606 will have on our financial statements. For each revenue contract type, we have conducted a formal contract review process to evaluate the impact of ASC 606. We have substantially completed our evaluation. During the fourth quarter of 2017, we concluded on certain technical matters, including the evaluation of significant financing components and prepayments for services, resulting in no adjustment upon adoption. We continue to evaluate and develop disclosures required under the new standard, with a particular focus on the scope of contracts subject to disclosure of remaining performance obligations. Financial system and internal control changes necessary for adoption have been implemented effective as of January 1, 2018. We do not expect ASC 606 to have a material impact on the timing of our revenue recognition.

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Contingent Liabilities and Commitments (Notes)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Contingent Liabilities and Commitments

CONTINGENT LIABILITIES AND COMMITMENTS

Rate Matters

General rate case (Docket No. RP06-569) On August 31, 2006, we submitted to the FERC a general rate filing principally designed to recover increased costs. The rates became effective March 1, 2007, subject to refund and the outcome of a hearing. All issues in this proceeding except one were resolved by settlement.

The one issue reserved for litigation or further settlement related to our proposal to change the design of the rates for service under our WSS-OA storage rate schedule, which was implemented subject to refund on March 1, 2007. Following a hearing, the FERC issued an opinion approving our proposed incremental rate design, and subsequently denied requests for rehearing of that approval. On February 21, 2014, the U. S. Court of Appeals for the D.C. Circuit (D.C. Circuit) issued an opinion that vacated and remanded the FERC's order because the FERC did not adequately support its conclusions. On March 17, 2016, the FERC issued an order addressing the issues raised by the D.C. Circuit's opinion. In the March 17 order, the FERC reversed its prior opinion and found that Transco's incremental rate design was unjust and unreasonable. The FERC directed Transco to design its WSS-OA rates on a rolled-in basis, to file revised WSS-OA rates reflecting the findings in the order, and to refund the amounts collected in excess of those rates since March 1, 2007. On April 18, 2016, we submitted the compliance filing reflecting rolled-in rates for WSS-OA service consistent with the March 17 order, and began charging those rates beginning April 19, 2016. We also filed a request for rehearing of the March 17 order. On October 4, 2017, the FERC issued an order denying all requests for rehearing of the March 17 order, accepting our April 18, 2016 compliance filing, and directing us to make refunds. No party filed a request for rehearing of the October 4 order, and no party filed an appeal of the March 17, 2016 or October 4, 2017 order. On November 16, 2017, we issued refunds of $19.2 million to the affected customers.

The rates we charge to our customers are subject to the rate-making policies of the FERC. These policies permit us to include in our cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Reform, makes significant changes to the U.S. federal income tax rules applicable to both individuals and entities, including among other things, a reduction in corporate federal income tax rates. Although we expect that the decreased federal income tax rates will require us to return amounts to certain customers in the future and as a result we recognized a regulatory liability as of the date of enactment of Tax Reform, the details of any regulatory implementation guidance remain uncertain.

Station 62 Incident

On October 8, 2015, an explosion and fire occurred at our Compressor Station No. 62 in Gibson, Louisiana. At the time of the incident, planned facility maintenance was being performed at the station and the facility was not operational. The incident was related to maintenance work being performed on the slug catcher at the station. Four contractor employees were killed in the incident and others were injured.

In responding to the incident, we cooperated with local, state and federal authorities, including the Louisiana State Police, Terrebonne Parish, the Louisiana Department of Environmental Quality, the U.S. Environmental Protection Agency (Region 6), the Occupational Safety and Health Administration, and the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA). On July 29, 2016, PHMSA issued a Notice of Probable Violation (NOPV), which includes a $1.6 million proposed civil penalty to us in connection with the incident. This penalty was accrued in the second quarter of 2016 and would not be covered by our insurance policies. We filed a response to the NOPV on August 25, 2016, and on July 14, 2017, PHMSA held a hearing on the NOPV.

The incident did not cause any rupture of the gas pipeline or any damage to the building containing the compressor engines. In anticipation of the planned maintenance, our Southeast Louisiana Lateral was taken out of service on October 4, 2015, which affected approximately 200 MMcf/d of natural gas production. The lateral was restored to service in early 2016 after repairs were made to the facilities damaged in the incident.

We are a defendant in lawsuits seeking damages for wrongful death, personal injury and property damages. We believe it is reasonably possible that losses will be incurred on some lawsuits. However, in management's judgment, the ultimate resolution of these matters will not have a material effect on our financial condition, results of operations or cash flows. While we also have claims for indemnification, we believe that it is probable that any ultimate losses incurred will be covered by our general liability insurance policy.

Environmental Matters

We have had studies underway for many years to test some of our facilities for the presence of toxic and hazardous substances such as polychlorinated biphenyls (PCBs) and mercury to determine to what extent, if any, remediation may be necessary. We have also similarly evaluated past on-site disposal of hydrocarbons at a number of our facilities. We have worked closely with and responded to data requests from the U.S. Environmental Protection Agency (EPA) and state agencies regarding such potential contamination of certain of our sites. On the basis of the findings to date, we estimate that environmental assessment and remediation costs under various federal and state statutes will total approximately $6 million to $8 million (including both expense and capital expenditures), measured on an undiscounted basis, and will substantially be spent over the next four to six years. This estimate depends on a number of assumptions concerning the scope of remediation that will be required at certain locations and the cost of the remedial measures. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs. At December 31, 2017, we had a balance of approximately $4.0 million for the expense portion of these estimated costs, $1.8 million recorded in Accrued liabilities - Other and $2.2 million recorded in Other Long-Term Liabilities - Other in the accompanying Consolidated Balance Sheet. At December 31, 2016, we had a balance of approximately $4.2 million for the expense portion of these estimated costs, $2.1 million recorded in Accrued liabilities - Other and $2.1 million recorded in Other Long-Term Liabilities - Other in the accompanying Consolidated Balance Sheet.

We have been identified as a potentially responsible party (PRP) at various Superfund and state waste disposal sites. Based on present volumetric estimates and other factors, our estimated aggregate exposure for remediation of these sites is less than $0.5 million. The estimated remediation costs for all of these sites are included in the $6 million to $8 million range discussed above. Liability under the Comprehensive Environmental Response, Compensation and Liability Act and applicable state law can be joint and several with other PRPs. Although volumetric allocation is a factor in assessing liability, it is not necessarily determinative; thus, the ultimate liability could be substantially greater than the amounts described above.

The EPA and various state regulatory agencies routinely promulgate and propose new rules, and issue updated guidance to existing rules. More recent rules and rulemakings include, but are not limited to, rules for reciprocating internal combustion engine maximum achievable control technology, air quality standards for one hour nitrogen dioxide emissions, and volatile organic compound and methane new source performance standards impacting design and operation of storage vessels, pressure valves, and compressors. On October 1, 2015, the EPA issued its rule regarding National Ambient Air Quality Standards for ground-level ozone, setting a stricter standard of 70 parts per billion. We are monitoring the rule’s implementation as the reduction will trigger additional federal and state regulatory actions that may impact our operations. Implementation of the regulations is expected to result in impacts to our operations and increase the cost of additions to Total property, plant and equipment, net in the Consolidated Balance Sheet for both new and existing facilities in affected areas. We are unable to reasonably estimate the cost of additions that may be required to meet the regulations at this time due to uncertainty created by various legal challenges to these regulations and the need for further specific regulatory guidance.

We consider prudently incurred environmental assessment and remediation costs and the costs associated with compliance with environmental standards to be recoverable through rates. To date, we have been permitted recovery of environmental costs, and it is our intent to continue seeking recovery of such costs through future rate filings. As a result, as estimated costs of environmental assessment and remediation are incurred, they are recorded as regulatory assets in the Consolidated Balance Sheet until collected through rates. At December 31, 2017, we had a balance of approximately $2.2 million of uncollected environmental related regulatory assets, $1.2 million recorded in Current Assets - Regulatory assets and $1.0 million recorded in Other Assets - Regulatory assets in the accompanying Consolidated Balance Sheet. At December 31, 2016, we had a balance of approximately $2.5 million of uncollected environmental related regulatory assets, $1.2 million recorded in Current Assets - Regulatory assets and $1.3 million recorded in Other Assets - Regulatory assets in the accompanying Consolidated Balance Sheet.

Other Matters

Various other proceedings are pending against us and are considered incidental to our operations.

Summary

We estimate that for all matters for which we are able to reasonably estimate a range of loss, including those noted above and others that are not individually significant, our aggregate reasonably possible losses beyond amounts accrued for all of our contingent liabilities are immaterial to our expected future annual results of operations, liquidity and financial position. These calculations have been made without consideration of any potential recovery from third parties. We have disclosed all significant matters for which we are unable to reasonably estimate a range of possible loss.

Other Commitments

Commitments for construction We have commitments for construction and acquisition of property, plant and equipment of approximately $114 million at December 31, 2017.

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Debt, Financing Arrangements and Leases (Notes)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Debt, Financing Arrangements and Leases

DEBT, FINANCING ARRANGEMENTS AND LEASES

Long-Term Debt

At December 31, 2017 and 2016, long-term debt outstanding was as follows (in thousands):

	2017			2016
Debentures:
7.08% due 2026	$	7,500		$	7,500
7.25% due 2026	200,000			200,000
Total debentures	207,500			207,500
Notes:
6.05% due 2018	250,000			250,000
7.85% due 2026	1,000,000			1,000,000
5.4% due 2041	375,000			375,000
4.45% due 2042	400,000			400,000
Total notes	2,025,000			2,025,000
Other financing obligation	230,926			—
Total long-term debt, including current portion	2,463,426			2,232,500
Unamortized debt issuance costs	(15,377		)	(16,408		)
Unamortized debt premium and discount, net	(5,043		)	(5,338		)
Long-term debt due within one year	(251,430		)	—
Total long-term debt	$	2,191,576		$	2,210,754

Aggregate minimum maturities (face value) applicable to long-term debt outstanding at December 31, 2017, for the next five years, are as follows (in thousands):

2018:     6.05% Notes and other financing obligation	$	251,566
2019:     Other financing obligation	$	1,721
2020:     Other financing obligation	$	1,893
2021:     Other financing obligation	$	2,081
2022:     Other financing obligation	$	2,289

No property is pledged as collateral under any of our long-term debt issues.

Restrictive Debt Covenants

At December 31, 2017, none of our debt instruments restrict the amount of distributions to our parent, provided, however, that under the credit facility described below, we are restricted from making distributions to our parent during an event of default if we have directly incurred indebtedness under the credit facility. Our debt agreements contain restrictions on our ability to incur secured debt beyond certain levels and to guarantee certain indebtedness. The indenture governing our $1 billion of 7.85% Senior Notes due 2026 further restricts our ability to guarantee certain indebtedness.

Issuance and Retirement of Long-Term Debt

On January 22, 2016, we issued $1 billion of 7.85 percent senior unsecured notes due 2026 to investors in a private debt placement. A portion of these proceeds was used to retire our $200 million of 6.4 percent notes that matured on April 15, 2016. We used the remainder for funding of capital expenditures. As part of the new issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. We were obligated to file and consummate a registration statement for an offer to exchange the notes for a new issue of substantially identical notes registered under the Securities Act, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. In January 2017, we completed an exchange of these notes for substantially identical new notes that are registered under the Securities Act.

Other Financing Obligation

During the construction of our Dalton Expansion Project, we received funding from a partner for its proportionate share of construction costs related to its undivided ownership interest in the Dalton lateral. Amounts received were recorded in Advances for construction costs and 100 percent of the costs associated with construction were capitalized on our Consolidated Balance Sheet. Upon placing the project in service during the third quarter of 2017, we began leasing this partner's undivided interest in the lateral, including the associated pipeline capacity, and reclassified approximately $235.8 million of funding previously received from our partner from Advances for construction costs to Long-Term Debt on our Consolidated Balance Sheet to reflect the financing obligation payable to our partner over an expected term of 35 years. At December 31, 2017, the amount included in Long-Term Debt on our Consolidated Balance Sheet for financing obligation is $229.4 million. As this transaction did not meet the criteria for sale leaseback accounting due to our continued involvement, it was accounted for as a financing arrangement over the course of the capacity agreement. The obligation matures in July 2052, requires monthly interest and principal payments, and bears an interest rate of approximately 10 percent.

Long-Term Debt Due Within One Year

The long-term debt due within one year at December 31, 2017 is associated with the $250 million of 6.05 percent notes maturing on June 15, 2018 and with the previously described other financing obligation.

Credit Facility

On February 2, 2015, we along with WPZ, Northwest, the lenders named therein and an administrative agent entered into the Second Amended & Restated Credit Agreement with aggregate commitments available of $3.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. In November 2017, the maturity date of the facility was extended to February 2, 2021. However, the co-borrowers may request an additional extension of the maturity date for a one year period to allow a maturity date as late as February 2, 2022, under certain circumstances. The agreement allows for swing line loans up to aggregate amount of $150 million, subject to available capacity under the credit facility, and letters of credit commitments available to WPZ of $1.125 billion. We are able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At December 31, 2017, no letters of credit have been issued and no loans to WPZ were outstanding under the credit facility.

Measured as of December 31, 2017, we are in compliance with our financial covenant under the credit facility.

Various covenants may limit, among other things, a borrower's and its material subsidiaries' ability to grant certain liens supporting indebtedness, merge or consolidate, sell all or substantially all of its assets, enter into certain affiliate transactions, make certain distributions during an event of default, enter into certain restrictive agreements, and allow any material change in the nature of its business.

If an event of default with respect to a borrower occurs under the credit facility, the lenders will be able to terminate the commitments for the respective borrowers and accelerate the maturity of any loans of the defaulting borrower under the credit facility agreement and exercise other rights and remedies.

Other than swing line loans, each time funds are borrowed, the borrower must choose whether such borrowing will be an alternate base rate borrowing or a Eurodollar borrowing. If such borrowing is an alternate base rate borrowing, interest is calculated on the basis of the greater of (a) the Prime Rate, (b) the Federal Funds Effective Rate plus one half of 1 percent and (c) a periodic fixed rate equal to the London Interbank Offered Rate (LIBOR) plus 1 percent, plus, in the case of each of (a), (b) and (c), an applicable margin. If the borrowing is a Eurodollar borrowing, interest is calculated on the basis of LIBOR for the relevant period plus an applicable margin. Interest on swing line loans is calculated as the sum of the alternate base rate plus an applicable margin. The borrower is required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin and the commitment fee are determined for each borrower by reference to a pricing schedule based on such borrower's senior unsecured long-term debt ratings.

WPZ participates in a commercial paper program and WPZ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. The program allows a maximum outstanding amount at any time of $3 billion of unsecured commercial paper notes. At December 31, 2017, WPZ had no outstanding commercial paper.

Lease Obligations

The future minimum lease payments under our various operating leases are as follows (in thousands):

2018	$	13,558
2019	14,890
2020	14,860
2021	14,710
2022	14,654
Thereafter	122,333
Total net minimum obligations	$	195,005

Our lease expense was $11.0 million in 2017, $10.6 million in 2016, and $10.7 million in 2015.

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ARO Trust (Notes)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

ARO Trust

ARO TRUST

Available-for-Sale Investments

We are entitled to collect in rates the amounts necessary to fund our ARO. We deposit monthly, into an external trust account (ARO Trust), the revenues specifically designated for ARO. The ARO Trust carries a moderate risk portfolio. We measure the financial instruments held in our ARO Trust at fair value. However, in accordance with the ASC Topic 980, Regulated Operations, both realized and unrealized gains and losses of the ARO Trust are recorded as regulatory assets or liabilities.

Effective March 1, 2013, the annual funding obligation is approximately $36.4 million, with deposits made monthly.

Investments in available-for-sale securities within the ARO Trust at fair value were as follows (in millions):

	December 31, 2017				December 31, 2016
	Amortized Cost Basis		Fair Value		Amortized Cost Basis		Fair Value
Cash and Money Market Funds	$	12.6	$	12.6	$	5.0	$	5.0
U.S. Equity Funds	35.9		50.5		29.4		36.5
International Equity Funds	20.7		24.6		19.2		18.6
Municipal Bond Funds	46.8		46.9		36.7		36.3
Total	$	116.0	$	134.6	$	90.3	$	96.4

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Fair Value Measurements (Notes)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

FAIR VALUE MEASUREMENTS

The following table presents, by level within the fair value hierarchy, certain of our financial assets and liabilities. The carrying values of cash, short-term financial assets (advances to affiliate) that have variable interest rates, accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments. Therefore, these assets and liabilities are not presented in the following table.

							Fair Value Measurements Using
	Carrying Amount			Fair Value			Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
							(Millions)
Assets (liabilities) at December 31, 2017:
Measured on a recurring basis:
ARO Trust investments	$	134.6		$	134.6		$	134.6	$	—		$	—
Additional disclosures:
Long-term debt, including current portion	(2,443.0		)	(3,103.3		)	—		(3,103.3		)	—
Assets (liabilities) at December 31, 2016:
Measured on a recurring basis:
ARO Trust investments	$	96.4		$	96.4		$	96.4	$	—		$	—
Additional disclosures:
Long-term debt	(2,210.8		)	(2,507.5		)	—		(2,507.5		)	—

Fair Value of Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

ARO Trust investments - We deposit a portion of our collected rates, pursuant to the terms of the Docket No. RP12-993 rate case settlement, into the ARO Trust which is specifically designated to fund future asset retirement obligations. The ARO Trust invests in a portfolio of actively traded mutual funds that are measured at fair value on a recurring basis based on quoted prices in an active market, are classified as available-for-sale and are reported in Other Assets-Other in the Consolidated Balance Sheet. However, both realized and unrealized gains and losses are ultimately recorded as regulatory assets or liabilities. See Note 4 for more information regarding the ARO Trust.

Long-term debt - The disclosed fair value of our long-term debt is determined primarily by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The fair value of the financing obligation associated with our Dalton lateral, which is included within long-term debt, was determined using an income approach (See Note 3 - Debt and Financing Agreements).

Reclassifications of fair value between Level 1, Level 2, and Level 3 of the fair value hierarchy, if applicable, are made at the end of each quarter. No transfers between Level 1 and Level 2 occurred during the year ended December 31, 2017 or 2016.

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Benefit Plans (Notes)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Benefit Plans

BENEFIT PLANS

Certain of the benefit costs charged to us by Williams associated with employees who directly support us are described below. Additionally, allocated corporate expenses from Williams to us also include amounts related to these same employee benefits, which are not included in the amounts presented below.

Pension and Other Postretirement Benefit Plans

Williams has noncontributory defined benefit pension plans (Williams Pension Plan, Williams Inactive Employees Pension Plan and The Williams Companies Retirement Restoration Plan) that provide pension benefits for its eligible employees. Pension cost charged to us by Williams was $15.6 million, $8.7 million and $13.5 million for 2017, 2016, and 2015, respectively. Included in our 2017 pension costs is a $7.6 million settlement charge. This amount reflects the portion of Williams’ settlement charge directly charged to us which was required as a result of lump-sum benefit payments made under Williams’ 2017 program to pay out certain deferred vested pension benefits, as well as lump-sum benefit payments made throughout 2017. In addition, we were charged $4.6 million of allocated corporate expenses also associated with the settlement charge.

Williams makes annual cash contributions to the pension plans, based on annual actuarial estimates, which Transco recovers through rates that are set through periodic general rate filings. Effective with the RP12-993 Settlement, any amounts of annual contributions that exceed an upper threshold or fall below a lower threshold are recorded as adjustments to income and collected or refunded through future rate adjustments. The amount of deferred pension collections recorded as a regulatory liability at December 31, 2017 and 2016 were $32.5 million and $21.3 million, respectively.

Williams provides subsidized retiree health care and life insurance benefits to certain eligible participants. Generally, participants that were employed by Williams on or before December 31, 1991 or December 31, 1995, if they were employees or retirees of Transco Energy Company and its subsidiaries, are eligible for subsidized retiree health care benefits. We recognized other postretirement benefit income of $10.9 million, $12.0 million and $11.9 million for 2017, 2016, and 2015, respectively.

We have been allowed by rate case settlements to collect or refund in future rates any differences between the actuarially determined costs and amounts currently being recovered in rates related to other postretirement benefits. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as an adjustment to expense and collected or refunded through future rate adjustments. The amount of other postretirement benefits costs deferred as a regulatory liability at December 31, 2017 and 2016 are $73.9 million and $63.0 million, respectively. These amounts are comprised of amounts being deferred for future rate treatment of $65.4 million and $52.0 million at December 31, 2017 and 2016, respectively, and amounts of $8.5 million and $11.0 million being amortized over a period of approximately 8 years per Docket No. RP12-993 at December 31, 2017 and 2016, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $7.7 million, $6.5 million and $6.6 million in 2017, 2016 and 2015, respectively, for Williams’ company matching contributions to this plan.

Employee Stock-Based Compensation Plan Information

The Williams Companies, Inc. 2007 Incentive Plan, as subsequently amended and restated, (Plan) provides for Williams’ common stock based awards to both employees and non-management directors. The Plan permits the granting of various types of awards including, but not limited to, restricted stock units and stock options. Awards may be granted for no consideration other than prior and future services or based on certain financial performance targets achieved.

Williams currently bills us directly for compensation expense related to stock-based compensation awards based on the fair value of the awards. We are also billed for our proportionate share of Williams’ and other affiliates’ stock-based compensation expense through various allocation processes.

Total stock-based compensation expense for the years ended December 31, 2017, 2016, and 2015 was $5.7 million, $4.0 million and $4.0 million, respectively, excluding amounts allocated from WPZ and Williams.

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Transactions with Major Customers and Affiliates (Notes)

12 Months Ended

Dec. 31, 2017

Transactions with Major Customers and Affiliates [Abstract]

Transactions with Major Customers and Affiliates

TRANSACTIONS WITH MAJOR CUSTOMERS AND AFFILIATES

Major Customers

Operating revenues received from three of our major customers in 2017, 2016 and 2015 are as follows (in millions):

	2017		2016		2015
Duke Energy Corporation	$	198.4	$	178.9	$	94.6
National Grid	177.4		166.3		129.6
The Southern Company, Inc.	160.0		69.6		61.6

Affiliates

We are a participant in WPZ’s cash management program, and we make advances to and receive advances from WPZ. At December 31, 2017 and 2016, our advances to WPZ totaled approximately $395.2 million and $811.7 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate in the accompanying Consolidated Balance Sheet. Advances are stated at the historical carrying amounts. Interest income is recognized when chargeable and collectability is reasonably assured. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on WPZ’s excess cash at the end of each month. At December 31, 2017, the interest rate was 1.16 percent.

Included in Operating Revenuesin the accompanying Consolidated Statement of Comprehensive Income for 2017, 2016 and 2015 are revenues received from affiliates of $10.3 million, $11.2 million, and $4.6 million, respectively. The rates charged to provide sales and services to affiliates are the same as those that are charged to similarly-situated nonaffiliated customers.

Included in Cost of natural gas sales in the accompanying Consolidated Statement of Comprehensive Income for 2017, 2016 and 2015 is purchased gas cost from affiliates of $3.9 million, $4.3 million, and $6.0 million, respectively. All gas purchases are made at market or contract prices.

We have no employees. Services necessary to operate our business are provided to us by Williams and certain affiliates of Williams. We reimburse Williams and its affiliates for all direct and indirect expenses incurred or payments made (including salary, bonus, incentive compensation and benefits) in connection with these services. Employees of Williams also provide general, administrative and management services to us, and we are charged for certain administrative expenses incurred by Williams. These charges are either directly identifiable or allocated to our assets. Direct charges are for goods and services provided by Williams at our request. Allocated charges are based on a three-factor formula, which considers revenues; property, plant and equipment; and payroll. In management’s estimation, the allocation methodologies used are reasonable and result in a reasonable allocation to us of our costs of doing business incurred by Williams. We were billed $370.4 million, $318.4 million, and $327.1 million during 2017, 2016 and 2015, respectively, for these services. Such expenses are primarily included in Administrative and general and Operation and maintenance expenses in the accompanying Consolidated Statement of Comprehensive Income. The amount billed to us during 2016 includes $7.4 million for severance and other related costs associated with a reduction in workforce primarily recognized in the first quarter.

We provide services to certain of our affiliates. We recorded reductions in operating expenses for services provided to and reimbursed by our affiliates of $3.7 million, $4.3 million, and $5.7 million in 2017, 2016 and 2015, respectively.

We made equity distributions of $430 million, $440 million and $536 million during 2017, 2016 and 2015, respectively.

During 2017, 2016 and 2015, our parent made contributions totaling $410 million, $502 million and $652 million, respectively, to us to fund a portion of our expenditures for additions to property, plant and equipment.

During July 2017, we recorded deferred revenue and recognized a non-cash distributionto our parent of $240 million associated with funds received by WPZ related to the March 2016 WPZ agreement with the member-sponsors of Sabal Trail regarding the Hillabee Expansion and Sabal Trail projects. Although the agreement was between WPZ and the member-sponsors, since the agreement was, in part, related to furthering the completion of Hillabee, this deferred revenue is assigned to our results of operations over the 25-year term of the capacity agreement with Sabal Trail.

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Asset Retirement Obligations (Notes)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

ASSET RETIREMENT OBLIGATIONS

These accrued obligations relate to underground storage caverns, offshore platforms, pipelines, and gas transmission facilities. At the end of the useful life of each respective asset, we are legally obligated to plug storage caverns and remove any related surface equipment, to dismantle offshore platforms, to cap certain gathering pipelines at the wellhead connection and remove any related surface equipment, and to remove certain components of gas transmission facilities from the ground.

During 2017 and 2016, our overall asset retirement obligation changed as follows (in thousands):

	2017			2016
Beginning balance	$	275,452		$	323,026
Accretion (1)	104,659			35,740
New obligations	28,447			7,995
Changes in estimates of existing obligations (2)	(38,470		)	(85,514		)
Property dispositions/obligations settled	(6,132		)	(5,795		)
Ending balance	$	363,956		$	275,452

(1) The increase in accretion for 2017 includes the cumulative effect of accretion adjustment associated with new AROs identified in our historical land agreements of $87 million that are not a component of new obligations.

(2) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal cost, discount rates, and the estimated remaining life of assets. The changes in estimates of existing obligations reflect a decrease of $38 million and $86 million for 2017 and 2016, respectively. The decrease in 2017 is primarily due to a decrease in current estimates for offshore removal costs. The decrease in 2016 is due primarily to revisions in the estimated remaining life of assets and the current estimate to the inflation rate.

We are entitled to collect in rates the amounts necessary to fund our ARO. All funds received for such retirements are deposited into an external trust account dedicated to funding our ARO. Under our current rate settlement our annual funding obligation is approximately $36.4 million, with installments to be deposited monthly (See Note 4).

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Regulatory Assets and Liabilities (Notes)

12 Months Ended

Dec. 31, 2017

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory Assets and Liabilities

REGULATORY ASSETS AND LIABILITIES

The regulatory assets and regulatory liabilities resulting from our application of the provisions of ASC Topic 980, Regulated Operations, included in the accompanying Consolidated Balance Sheet at December 31, 2017 and December 31, 2016 are as follows (in millions):

Regulatory Assets	2017		2016
Grossed-up deferred taxes on equity funds used during construction	$	37.9	$	73.2
Asset retirement obligations	168.7		117.2
Asset retirement costs - Eminence	49.5		53.9
Deferred taxes - asset	3.8		4.8
Deferred cash out	42.5		48.2
Deferred gas costs	6.0		—
Fuel cost	61.4		51.3
Other	3.7		2.5
Total Regulatory Assets	$	373.5	$	351.1

Regulatory Liabilities	2017		2016
Negative salvage	$	409.7	$	357.1
Deferred taxes - liability	471.1		—
Sentinel meter station depreciation	6.3		6.2
Postretirement benefits other than pension	73.9		63.0
Electric power cost	13.3		6.3
Pension - deferred collections	32.5		21.3
Other	0.3		4.6
Total Regulatory Liabilities	$	1,007.1	$	458.5

The significant regulatory assets and liabilities include:

Grossed-up deferred taxes on equity funds used during construction: Regulatory asset balance established to offset the deferred tax for the equity component of the allowance for funds used during the construction of long-lived assets. All amounts were generated during the period that we were a taxable entity. Taxes on capitalized funds used during construction and the offsetting deferred income taxes are included in the rate base and are recovered over the depreciable lives of the long-lived asset to which they relate.

Asset retirement obligations: Regulatory asset balance established to offset depreciation of the ARO asset and changes in the ARO liability due to the passage of time. The regulatory asset is being recovered through our rates, and is being amortized to expense consistent with the amounts collected in rates (See Note 8).

Asset retirement costs - Eminence: Regulatory asset balance associated with the Eminence Storage Field retirement costs. The regulatory asset is being recovered through our rates, and is being amortized to expense consistent with the amounts collected in rates.

Deferred taxes - asset: Regulatory asset balance was established as a result of an increase to rate base deferred taxes due to an increase to the effective state income tax rate. The regulatory asset is being collected from rate payers over the remaining depreciable lives of the long-lived asset to which they relate.

Deferred cash out: This amount represents the deferral of gains or losses on the purchases and sales of gas imbalances with shippers. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual cash out filing periods.

Deferred gas costs: This amount arises from the movement of gas volumes between gas inventory accounts that have different valuations. These amounts are expected to be recovered/refunded in subsequent periods.

Fuel cost: This amount represents the difference between the gas retained from our customers and the gas consumed in operations. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual fuel tracker filing periods.

Negative salvage: Our rates include a component designed to recover certain future retirement costs for which we are not required to record an asset retirement obligation. We record a regulatory liability representing the cumulative residual amount of recoveries through rates, net of expenditures associated with these retirement costs.

Sentinel meter station depreciation: This amount reflects the incremental depreciation being recorded related to the meter station modifications made for three of the Sentinel shippers. These modifications will be recovered through a surcharge over a defined period of time as stated in the Sentinel FERC order. The incremental depreciation represents the difference between the FERC granted depreciation rate for such facilities in the last rate case as compared to the depreciation rates in the Sentinel order which are based on the contractual terms in the surcharge agreements. The incremental depreciation will be recorded through the end of the contractual term and then will be amortized.

Postretirement benefits: We recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any difference between the annual actuarially determined cost and the amount recovered in rates is recorded as a regulatory asset or liability to be collected or refunded through future rate adjustments. These amounts are not included in the rate base (See Note 6).

Electric power cost: This amount represents the difference between the electric power costs recovered from our customers and the electric power costs incurred in operations. These amounts are not included in the rate base but are expected to be recovered/refunded in subsequent annual electric power tracker filing periods.

Pension - deferred collections: We recover the actuarially determined pension cash contributions through rates that are set through periodic general rate filings. Effective with the RP12-993 Settlement, any amounts of annual contributions that exceed an upper threshold or fall below a lower threshold are recorded as adjustments to income and collected or refunded through future rate adjustments (See Note 6).

Deferred taxes - liability: Regulatory liability balance was established as a result of a decrease to rate base deferred taxes due to a decrease to the effective federal income tax rate. The timing of the refund of the regulatory liability to rate payers will be subject to future discussions and negotiations with our customers in our next rate case.

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Other (Notes)

12 Months Ended

Dec. 31, 2017

Other Income and Expenses [Abstract]

Other

OTHER

During 2017 and 2016, we capitalized $0.2 million and $1.4 million, respectively, of project feasibility costs, which had been expensed in prior periods in Other expense, net, upon determining that the project was probable of development.

The Advances for construction costs on the Consolidated Balance Sheet are associated with advances received from third parties related to construction costs on the Atlantic Sunrise and Dalton projects. This balance increases as we receive additional advances. After construction of the respective projects are completed, the related liabilities will be reclassified to Long-Term Debt and reduced by payments we make to the third parties under terms of the applicable lease agreements. In the third quarter of 2017, the advances received from a third party related to construction costs on the Dalton lateral was reclassified to Long-Term Debt on our Consolidated Balance Sheet.

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Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Regulatory Accounting

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). The Accounting Standards Codification (ASC) Regulated Operations (Topic 980), provides that rate-regulated public utilities account for and report regulatory assets and liabilities consistent with the economic effect of the way in which regulators establish rates if the rates established are designed to recover the costs of providing the regulated service and if the competitive environment makes it probable that such rates can be charged and collected. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, employee related benefits, environmental costs, negative salvage, asset retirement obligations (ARO), and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980 and, accordingly, the accompanying consolidated financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

In December 2017, the Tax Cuts and Jobs Act was enacted, which, among other things, reduced the federal corporate income tax rate from 35 percent to 21 percent (Tax Reform). In accordance with ASC 980-740-25-2, we have recognized a regulatory liability to reflect the probable return to certain customers through future rates of the future decrease in income taxes payable associated with Tax Reform. In determining the estimated liability that we currently believe is probable of return to certain customers through future rates, we considered the mix of services provided by us, taking into consideration that certain of these services are provided under contractually based rates, in lieu of recourse-based rates, that are designed to recover the cost of providing those services, with no expected future rate adjustment for the term of those contracts. The liability was recorded in December 2017 through a regulatory charge to operating income of $471.1 million. The timing and actual amount of such return will be subject to future negotiations regarding this matter and many other elements of cost-of-service rate proceedings, including other costs of providing service.

Certain of our equity-method investees recorded similar regulatory liabilities, for which our Equity in (earnings) loss of unconsolidated affiliates on our Consolidated Statement of Comprehensive Income has been reduced by $10.3 million related to our proportionate share of the associated regulatory charges.

Our regulatory asset associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $32.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net on our Consolidated Statement of Comprehensive Income.

Basis of Presentation

Basis of Presentation

Williams’ acquisition of Transco Energy Company and its subsidiaries, including us, in 1995 was accounted for using the purchase method of accounting. Accordingly, an allocation of the purchase price was assigned to our assets and liabilities based on their estimated fair values. The purchase price allocation to us primarily consisted of a $1.5 billion allocation to property, plant and equipment and adjustments to deferred taxes based upon the book basis of the net assets recorded as a result of the acquisition. The amount allocated to property, plant and equipment is being depreciated on a straight-line basis over 40 years, the estimated useful lives of these assets at the date of acquisition, at approximately $35 million per year. At December 31, 2017, the remaining property, plant and equipment allocation was approximately $0.6 billion. Current FERC policy does not permit us to recover through rates amounts in excess of original cost.

Principles of Consolidation

Principles of Consolidation

The consolidated financial statements include our accounts and the accounts of the subsidiaries we control. Companies in which we and our subsidiaries own 20 percent to 50 percent of the voting common stock or otherwise exercise significant influence over operating and financial policies of the company are accounted for under the equity method. The equity method investments as of December 31, 2017 and December 31, 2016 consist of Cardinal Pipeline Company, LLC (Cardinal) with ownership interest of approximately 45 percent and Pine Needle LNG Company, LLC (Pine Needle) with ownership interest of 35 percent. We received distributions associated with our equity method investments totaling $8.0 million, $8.6 million, and $7.6 million in 2017, 2016 and 2015, respectively. Included in the distributions are $3.9 million, $2.8 million and $2.0 million return of capital in 2017, 2016 and 2015, respectively.

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Estimates and assumptions which, in the opinion of management, are significant to the underlying amounts included in the financial statements and for which it would be reasonably possible that future events or information could change those estimates include: 1) revenues subject to refund; 2) litigation-related contingencies; 3) environmental remediation obligations; 4) impairment assessments of long-lived assets; 5) depreciation; 6) asset retirement obligations; and 7) regulatory deferred taxes.

Revenue Recognition

Revenue Recognition

Revenues for transportation of gas under long-term firm agreements are recognized considering separately the reservation and commodity charges. Reservation revenues are recognized monthly over the term of the agreement regardless of the volume of natural gas transported. Commodity revenues from both firm and interruptible transportation are recognized in the period transportation services are provided based on volumes of natural gas physically delivered at the agreed upon delivery point. Revenues for the storage of gas under firm agreements are recognized considering separately the reservation, capacity, and injection and withdrawal charges. Reservation and capacity revenues are recognized monthly over the term of the agreement regardless of the volume of storage service actually utilized. Injection and withdrawal revenues are recognized in the period when volumes of natural gas are physically injected into or withdrawn from storage.

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. The resulting imbalances are primarily settled through the purchase and sale of gas with our customers under terms provided in our FERC tariff. Revenue is recognized from the sale of gas upon settlement of the transportation and exchange imbalances (See Gas Imbalances in this Note).

As a result of the ratemaking process, certain revenues collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel and other risks.

Environmental Matters

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that any expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

Property, Plant and Equipment

Property, Plant and Equipment

Property, plant and equipment is recorded at cost. The carrying values of these assets are also based on estimates, assumptions and judgments relative to capitalized costs, useful lives and salvage values. These estimates, assumptions and judgments reflect FERC regulations, as well as historical experience and expectations regarding future industry conditions and operations. The FERC identifies installation, construction and replacement costs that are to be capitalized. All other costs are expensed as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are credited or charged to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission facilities, production and gathering facilities and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC. Depreciation rates used for major regulated gas plant facilities at December 31, 2017, 2016 and 2015 are as follows:

Category of Property	2017-2015
Gathering facilities	1.35% - 2.50%
Storage facilities	2.10% -  2.25%
Onshore transmission facilities	2.61%  -  5.00%
Offshore transmission facilities	1.20%  -  1.20%

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurements of AROs include, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as a market-risk premium. The ARO asset is depreciated in a manner consistent with the expected timing of the future abandonment of the underlying physical assets. We measure changes in the liability due to passage of time by applying an interest method of allocation. The depreciation of the ARO asset and accretion of the ARO liability are recognized as an increase to a regulatory asset, as management expects to recover such amounts in future rates. The regulatory asset is amortized commensurate with our collection of these costs in rates.

Impairment of Long-Lived Assets

Impairment of Long-lived Assets

We evaluate the long lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. When an indicator of a potential impairment has occurred we compare our management’s estimate of undiscounted future cash flows attributable to the assets to the carrying value of the assets to determine whether an impairment has occurred. We apply a probability-weighted approach to consider the likelihood of different cash flow assumptions and possible outcomes including selling in the near term or holding for the remaining estimated useful life. If an impairment of the carrying value has occurred, we determine the amount of the impairment recognized in the financial statements by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

For assets identified to be disposed of in the future and considered held for sale in accordance with the ASC Property, Plant, and Equipment (Topic 360), we compare the carrying value to the estimated fair value less the cost to sell to determine if recognition of an impairment is required. Until the assets are disposed of, the estimated fair value, which includes estimated cash flows from operations until the assumed date of sale, is recalculated when related events or circumstances change.

Judgments and assumptions are inherent in our management’s estimate of undiscounted future cash flows used to determine recoverability of an asset and the estimate of an asset’s fair value used to calculate the amount of impairment to recognize.

Allowance for Funds Used During Construction

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and are included as a cost of property, plant and equipment because it constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $22.3 million, $12.5 million and $14.6 million, for 2017, 2016 and 2015, respectively. The allowance for equity funds was $69.7 million, $56.5 million, and $48.4 million, for 2017, 2016 and 2015, respectively.

Income Taxes

Income Taxes

We generally are not a taxable entity for federal or state and local income tax purposes. The tax on net income is generally borne by unitholders of our ultimate parent, WPZ. Net income for financial statement purposes may differ significantly from taxable income of WPZ’s unitholders as a result of differences between the tax basis and financial reporting basis of assets and liabilities and the taxable income allocation requirements under the WPZ partnership agreement. The aggregated difference in the basis of our assets for financial and tax reporting purposes cannot be readily determined because information regarding each of WPZ’s unitholder’s tax attributes in WPZ is not available to us.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts Receivable and Allowance for Doubtful Receivables

Accounts receivable are stated at the historical carrying amount net of reserves or write-offs. Our credit risk exposure in the event of nonperformance by the other parties is limited to the face value of the receivables. We perform ongoing credit evaluations of our customers’ financial condition and require collateral from our customers, if necessary. Due to our customer base, we have not historically experienced recurring credit losses in connection with our receivables. Receivables determined to be uncollectible are reserved or written off in the period of determination.

Gas Imbalances

Gas Imbalances

In the course of providing transportation services to customers, we may receive different quantities of gas from shippers than the quantities delivered on behalf of those shippers. Additionally, we transport gas on various pipeline systems which may deliver different quantities of gas on behalf of us than the quantities of gas received from us. These transactions result in gas transportation and exchange imbalance receivables and payables which are recovered or repaid in cash or through the receipt or delivery of gas in the future and are recorded in the accompanying Consolidated Balance Sheet. Settlement of imbalances requires agreement between the pipelines and shippers as to allocations of volumes to specific transportation contracts and timing of delivery of gas based on operational conditions. Our tariff includes a method whereby most transportation imbalances are settled on a monthly basis. Each month a portion of the imbalances are not identified to specific parties and remain unsettled. These are generally identified to specific parties and settled in subsequent periods. We believe that amounts that remain unidentified to specific parties and unsettled at year end are valid balances that will be settled with no material adverse effect upon our financial position, results of operations or cash flows. Management has implemented a policy of continuing to carry any unidentified transportation and exchange imbalances on the books for a three-year period. At the end of the three year period a final assessment will be made of their continued validity. Absent a valid reason for maintaining the imbalance, any remaining balance will be recognized in income. Certain imbalances are being recovered or repaid in cash or through the receipt or delivery of gas upon agreement of the parties as to the allocation of the gas volumes, and as permitted by pipeline operating conditions. These imbalances have been classified as current assets and current liabilities at December 31, 2017 and 2016. We utilize the average cost method of accounting for gas imbalances.

Deferred Cash Out

Most transportation imbalances are settled in cash on a monthly basis (cash out). We are required by our tariff to refund revenues received from the cash out of transportation imbalances in excess of costs incurred during the annual August through July reporting period. Revenues received in excess of costs incurred are deferred until refunded in accordance with the tariff.

Inventory

Gas Inventory

We utilize the last-in, first-out (LIFO) method of accounting for inventory gas in storage. At December 31, 2017 and 2016, Gas in Storage, at LIFO, was zero. The basis for determining current cost at the end of each year is the December monthly average gas price delivered to pipelines in Texas and Louisiana. We utilize the average cost method of accounting for gas available for customer nomination. Liquefied natural gas in storage is valued at original cost.

Materials and Supplies Inventory

All inventories are stated at lower of average cost or net realizable value. We perform an annual review of Materials and Supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2017 and 2016.

Contingent Liabilities

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans. (See Note 6.) Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us and thus paid by us, is based on our share of net periodic benefit cost.

Cash Equivalents

We include short-term, highly-liquid investments that have an original maturity of three months or less as cash equivalents.

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Fair Value Measurements (Policies)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair Value of Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

ARO Trust investments - We deposit a portion of our collected rates, pursuant to the terms of the Docket No. RP12-993 rate case settlement, into the ARO Trust which is specifically designated to fund future asset retirement obligations. The ARO Trust invests in a portfolio of actively traded mutual funds that are measured at fair value on a recurring basis based on quoted prices in an active market, are classified as available-for-sale and are reported in Other Assets-Other in the Consolidated Balance Sheet. However, both realized and unrealized gains and losses are ultimately recorded as regulatory assets or liabilities. See Note 4 for more information regarding the ARO Trust.

Long-term debt - The disclosed fair value of our long-term debt is determined primarily by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The fair value of the financing obligation associated with our Dalton lateral, which is included within long-term debt, was determined using an income approach (See Note 3 - Debt and Financing Agreements).

Reclassifications of fair value between Level 1, Level 2, and Level 3 of the fair value hierarchy, if applicable, are made at the end of each quarter. No transfers between Level 1 and Level 2 occurred during the year ended December 31, 2017 or 2016.

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Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Depreciation rates

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission facilities, production and gathering facilities and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC. Depreciation rates used for major regulated gas plant facilities at December 31, 2017, 2016 and 2015 are as follows:

Category of Property	2017-2015
Gathering facilities	1.35% - 2.50%
Storage facilities	2.10% -  2.25%
Onshore transmission facilities	2.61%  -  5.00%
Offshore transmission facilities	1.20%  -  1.20%

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Debt, Financing Arrangements and Leases (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-term debt

At December 31, 2017 and 2016, long-term debt outstanding was as follows (in thousands):

	2017			2016
Debentures:
7.08% due 2026	$	7,500		$	7,500
7.25% due 2026	200,000			200,000
Total debentures	207,500			207,500
Notes:
6.05% due 2018	250,000			250,000
7.85% due 2026	1,000,000			1,000,000
5.4% due 2041	375,000			375,000
4.45% due 2042	400,000			400,000
Total notes	2,025,000			2,025,000
Other financing obligation	230,926			—
Total long-term debt, including current portion	2,463,426			2,232,500
Unamortized debt issuance costs	(15,377		)	(16,408		)
Unamortized debt premium and discount, net	(5,043		)	(5,338		)
Long-term debt due within one year	(251,430		)	—
Total long-term debt	$	2,191,576		$	2,210,754

Maturities of long-term debt

Aggregate minimum maturities (face value) applicable to long-term debt outstanding at December 31, 2017, for the next five years, are as follows (in thousands):

2018:     6.05% Notes and other financing obligation	$	251,566
2019:     Other financing obligation	$	1,721
2020:     Other financing obligation	$	1,893
2021:     Other financing obligation	$	2,081
2022:     Other financing obligation	$	2,289

Future minimum lease payments

The future minimum lease payments under our various operating leases are as follows (in thousands):

2018	$	13,558
2019	14,890
2020	14,860
2021	14,710
2022	14,654
Thereafter	122,333
Total net minimum obligations	$	195,005

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ARO Trust (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

ARO Trust

Investments in available-for-sale securities within the ARO Trust at fair value were as follows (in millions):

	December 31, 2017				December 31, 2016
	Amortized Cost Basis		Fair Value		Amortized Cost Basis		Fair Value
Cash and Money Market Funds	$	12.6	$	12.6	$	5.0	$	5.0
U.S. Equity Funds	35.9		50.5		29.4		36.5
International Equity Funds	20.7		24.6		19.2		18.6
Municipal Bond Funds	46.8		46.9		36.7		36.3
Total	$	116.0	$	134.6	$	90.3	$	96.4

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Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of fair value, assets and liabilities measured on recurring basis

The following table presents, by level within the fair value hierarchy, certain of our financial assets and liabilities. The carrying values of cash, short-term financial assets (advances to affiliate) that have variable interest rates, accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments. Therefore, these assets and liabilities are not presented in the following table.

							Fair Value Measurements Using
	Carrying Amount			Fair Value			Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
							(Millions)
Assets (liabilities) at December 31, 2017:
Measured on a recurring basis:
ARO Trust investments	$	134.6		$	134.6		$	134.6	$	—		$	—
Additional disclosures:
Long-term debt, including current portion	(2,443.0		)	(3,103.3		)	—		(3,103.3		)	—
Assets (liabilities) at December 31, 2016:
Measured on a recurring basis:
ARO Trust investments	$	96.4		$	96.4		$	96.4	$	—		$	—
Additional disclosures:
Long-term debt	(2,210.8		)	(2,507.5		)	—		(2,507.5		)	—

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Transactions with Major Customers and Affiliates (Tables)

12 Months Ended

Dec. 31, 2017

Transactions with Major Customers and Affiliates [Abstract]

Schedule of revenue by major customers

Operating revenues received from three of our major customers in 2017, 2016 and 2015 are as follows (in millions):

	2017		2016		2015
Duke Energy Corporation	$	198.4	$	178.9	$	94.6
National Grid	177.4		166.3		129.6
The Southern Company, Inc.	160.0		69.6		61.6

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Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2017 and 2016, our overall asset retirement obligation changed as follows (in thousands):

	2017			2016
Beginning balance	$	275,452		$	323,026
Accretion (1)	104,659			35,740
New obligations	28,447			7,995
Changes in estimates of existing obligations (2)	(38,470		)	(85,514		)
Property dispositions/obligations settled	(6,132		)	(5,795		)
Ending balance	$	363,956		$	275,452

(1) The increase in accretion for 2017 includes the cumulative effect of accretion adjustment associated with new AROs identified in our historical land agreements of $87 million that are not a component of new obligations.

(2) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal cost, discount rates, and the estimated remaining life of assets. The changes in estimates of existing obligations reflect a decrease of $38 million and $86 million for 2017 and 2016, respectively. The decrease in 2017 is primarily due to a decrease in current estimates for offshore removal costs. The decrease in 2016 is due primarily to revisions in the estimated remaining life of assets and the current estimate to the inflation rate.

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Regulatory Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Regulatory Assets and Liabilities Disclosure [Abstract]

Schedule of Regulatory Assets [Table Text Block]

The regulatory assets and regulatory liabilities resulting from our application of the provisions of ASC Topic 980, Regulated Operations, included in the accompanying Consolidated Balance Sheet at December 31, 2017 and December 31, 2016 are as follows (in millions):

Regulatory Assets	2017		2016
Grossed-up deferred taxes on equity funds used during construction	$	37.9	$	73.2
Asset retirement obligations	168.7		117.2
Asset retirement costs - Eminence	49.5		53.9
Deferred taxes - asset	3.8		4.8
Deferred cash out	42.5		48.2
Deferred gas costs	6.0		—
Fuel cost	61.4		51.3
Other	3.7		2.5
Total Regulatory Assets	$	373.5	$	351.1

Schedule of Regulatory Liabilities [Table Text Block]

Regulatory Liabilities	2017		2016
Negative salvage	$	409.7	$	357.1
Deferred taxes - liability	471.1		—
Sentinel meter station depreciation	6.3		6.2
Postretirement benefits other than pension	73.9		63.0
Electric power cost	13.3		6.3
Pension - deferred collections	32.5		21.3
Other	0.3		4.6
Total Regulatory Liabilities	$	1,007.1	$	458.5

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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		$ 471,096	$ 0	$ 0
Purchase Price Allocation
Purchase price allocation, gross		$ 1,500,000
Purchase price allocation, property, plant and equipment, estimated useful lIfe		40 years
Purchase price allocation, depreciation		$ 35,000
Purchase price allocation, remaining allocation		600,000
Schedule of Equity Method Investments [Line Items]
Proceeds from Equity Method Investment, Distribution		8,000	8,600	7,600
Proceeds from Equity Method Investment, Distribution, Return of Capital		3,926	2,767	2,015
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, borrowed		22,300	12,500	14,600
Allowance for funds used during construction, equity		69,653	56,468	$ 48,435
Inventory Disclosure [Abstract]
Gas in storage, LIFO		0	0
Excess of replacement cost over LIFO cost		0	$ 0
Operating Expense [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		471,100
Nonoperating Income (Expense) [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		10,300
Other Nonoperating Income (Expense) [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		$ 32,700
Minimum
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent		21.00%
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Description of Principal Activities		.20
Maximum
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent		35.00%
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Description of Principal Activities		.50
Pine Needle LNG Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%	35.00%
Cardinal Pipeline Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		45.00%	45.00%
Financial Repositioning [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Parent, limited partner ownership percentage		74.00%
Parent, general partner ownership percentage	2.00%
Gathering facilities | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		1.35%	1.35%	1.35%
Gathering facilities | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		2.50%	2.50%	2.50%
Storage facilities | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		2.10%	2.10%	2.10%
Storage facilities | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		2.25%	2.25%	2.25%
Onshore transmission facilities | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		2.61%	2.61%	2.61%
Onshore transmission facilities | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		5.00%	5.00%	5.00%
Offshore transmission facilities | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		1.20%	1.20%	1.20%
Offshore transmission facilities | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation rates		1.20%	1.20%	1.20%

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Contingent Liabilities and Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Nov. 16, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Regulatory assets, total	$ 373,500		$ 351,100
Regulatory assets, current	97,149		87,059
Regulatory assets, noncurrent	276,315		264,001
Other Commitments [Abstract]
Commitments for construction and acquisition of property, plant, and equipment	114,000
Accrued Liabilities [Member]
Site Contingency [Line Items]
Notice of Penalty			1,600
Environmental assessment and remediation
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	4,000		4,200
Accrued environmental assessment and remediation costs, current	1,800		2,100
Accrued environmental assessment and remediation costs, noncurrent	2,200		2,100
Regulatory assets, total	2,200		2,500
Regulatory assets, current	1,200		1,200
Regulatory assets, noncurrent	1,000		$ 1,300
Environmental assessment and remediation | Minimum
Site Contingency [Line Items]
Environmental assessment and remediation costs, best estimate	$ 6,000
Expected duration of environmental assessment and remediation spending	4 years
Environmental assessment and remediation | Maximum
Site Contingency [Line Items]
Environmental assessment and remediation costs, best estimate	$ 8,000
Expected duration of environmental assessment and remediation spending	6 years
Potentially responsible party at various Superfund and state waste disposal sites | Maximum
Site Contingency [Line Items]
Environmental assessment and remediation costs, best estimate	$ 500
Settled Litigation [Member]
Site Contingency [Line Items]
Rate Settlement refund		$ 19,200

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Debt, Financing Arrangements and Leases (Details) - USD ($)		1 Months Ended	12 Months Ended
	Apr. 15, 2016	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 22, 2016	Feb. 02, 2015
Debt Instrument [Line Items]
Total long-term debt, including current portion			$ 2,463,426,000	$ 2,232,500,000
Other financing obligation			230,926,000	0
Unamortized debt issuance costs			(15,377,000)	(16,408,000)
Unamortized debt premium and discount, net			(5,043,000)	(5,338,000)
Long-term debt due within one year			251,430,000	0
Total long-term debt			2,191,576,000	2,210,754,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2018			251,566,000
2019			1,721,000
2020			1,893,000
2021			2,081,000
2022			2,289,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018			13,558,000
2019			14,890,000
2020			14,860,000
2021			14,710,000
2022			14,654,000
Thereafter			122,333,000
Total net minimum obligations			195,005,000
Operating leases, rent expense			11,000,000	10,600,000	$ 10,700,000
Williams Partners L.P. [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							$ 3,500,000,000
Additional amount by which credit facility can be increased							500,000,000
Line of Credit Facility, Remaining Borrowing Capacity							500,000,000
Commercial paper			$ 0
6.4% due 2016 [Member]
Debt Instrument [Line Items]
Long-term debt interest rate	6.40%
Long-Term Debt, retired	$ 200,000,000
10% due 2052 [Member]
Debt Instrument [Line Items]
Long-term debt interest rate			10.00%
Dalton Expansion Project [Member]
Debt Instrument [Line Items]
Other financing obligation		$ 235,800,000
Long-term debt face amount			$ 229,400,000
Debt Instrument, Term		35 years
Debentures
Debt Instrument [Line Items]
Total long-term debt, including current portion			207,500,000	207,500,000
Debentures | 7.08% due 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion			7,500,000	7,500,000
Debentures | 7.25% due 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion			200,000,000	200,000,000
Notes
Debt Instrument [Line Items]
Total long-term debt, including current portion			2,025,000,000	2,025,000,000
Notes | 6.05% due 2018 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion			250,000,000	250,000,000
Notes | 7.85% due 2026
Debt Instrument [Line Items]
Total long-term debt, including current portion			1,000,000,000	1,000,000,000
Long-term debt face amount						$ 1,000,000,000
Long-term debt interest rate						7.85%
Notes | 5.4% due 2041 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion			375,000,000	375,000,000
Notes | 4.45% due 2042 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion			400,000,000	$ 400,000,000
$3.5 billion credit facility [Member] | Williams Partners L.P. [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount			0
Line of credit facility, amount outstanding			$ 0
Swing Line Advances [Member] | Williams Partners L.P. [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							150,000,000
Commercial paper [Member] | Williams Partners L.P. [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							3,000,000,000
Letter of Credit [Member] | Williams Partners L.P. [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							$ 1,125,000,000

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ARO Trust (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Annual funding obligation	$ 36.4
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	116.0	$ 90.3
Available-for-sale securities, fair value	134.6	96.4
Cash And Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	12.6	5.0
Available-for-sale securities, fair value	12.6	5.0
U.S. Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	35.9	29.4
Available-for-sale securities, fair value	50.5	36.5
International Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	20.7	19.2
Available-for-sale securities, fair value	24.6	18.6
Municipal Bond Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	46.8	36.7
Available-for-sale securities, fair value	$ 46.9	$ 36.3

XML

Fair Value Measurements (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	$ 134,600,000	$ 96,400,000
Fair Value, Transfers Between Level 1 and Level 2, Description and Policy [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0	0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0	0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	0	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	0	0
Fair Value, Inputs, Level 1 [Member]
Additional Fair Value Elements [Abstract]
Long-term Debt, Fair Value	0	0
Fair Value, Inputs, Level 2 [Member]
Additional Fair Value Elements [Abstract]
Long-term Debt, Fair Value	(3,103,300,000)	(2,507,500,000)
Fair Value, Inputs, Level 3 [Member]
Additional Fair Value Elements [Abstract]
Long-term Debt, Fair Value	0	0
Reported Value Measurement [Member]
Additional Fair Value Elements [Abstract]
Long-term Debt, Fair Value	(2,443,000,000)	(2,210,800,000)
Estimate of Fair Value Measurement [Member]
Additional Fair Value Elements [Abstract]
Long-term Debt, Fair Value	(3,103,300,000)	(2,507,500,000)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	134,600,000	96,400,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	0	0
Fair Value, Measurements, Recurring [Member] | Reported Value Measurement [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	134,600,000	96,400,000
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
ARO Trust investments	$ 134,600,000	$ 96,400,000

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Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	$ 1,007.1	$ 458.5
Defined contribution plan, cost recognized	7.7	6.5	$ 6.6
Salaries, Wages and Officers' Compensation [Abstract]
Allocated share-based compensation expense	5.7	4.0	4.0
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension cost	15.6	8.7	13.5
Pension Plan [Member] | Directly charged [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension costs charges to us by Williams	7.6
Pension Plan [Member] | Allocated corporate expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension costs charges to us by Williams	4.6
Pension Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liability, deferred for future rate treatment	32.5	21.3
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liability, deferred for future rate treatment	65.4	52.0
Other postretirement benefit (income) expense	(10.9)	(12.0)	$ (11.9)
Regulatory liabilities	73.9	63.0
Regulatory liability, being amortized	$ 8.5	$ 11.0
Regulatory Liability, Amortization Period	8 years

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Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 395,247	$ 811,693
Related party transaction, rate		1.16%
Entity number of employees | employee		0
Expenses, related party		$ 370,400	318,400	$ 327,100
Severance Costs			7,400
Equity distributions		430,000	440,000	536,000
Cash contributions from parent		410,000	502,000	652,000
Duration Of Period For Deferred Revenue Recognition	25 years
Hillabee Expansion Project [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Additions	$ 240,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Operating revenues, related party		10,300	11,200	4,600
Purchases, related party		3,900	4,300	6,000
Expenses, related party		3,700	(4,300)	(5,700)
Williams Partners L.P. [Member]
Related Party Transaction [Line Items]
Advances to affiliate		395,200	811,700
Duke Energy Corporation [Member]
Revenue, Major Customer [Line Items]
Operating revenues		198,400	178,900	94,600
National Grid [Member]
Revenue, Major Customer [Line Items]
Operating revenues		177,400	166,300	129,600
The Southern Company, Inc [Member]
Revenue, Major Customer [Line Items]
Operating revenues		$ 160,000	$ 69,600	$ 61,600

XML

Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 275,452	$ 323,026
Accretion (1)	104,659	35,740
New obligations	28,447	7,995
Changes in estimates of existing obligations (2)	(38,470)	(85,514)
Property dispositions/obligations settled	(6,132)	(5,795)
Ending balance	363,956	275,452
Annual funding obligation	36,400
Asset retirement obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Changes in estimates of existing obligations (2)	(38,000)	$ (86,000)
Accretion (1)	87,000
External ARO trust [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Annual funding obligation	$ 36,400

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Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory assets	$ 373.5	$ 351.1
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,007.1	458.5
Negative salvage
Regulatory Liabilities [Line Items]
Regulatory liabilities	409.7	357.1
Deferred taxes
Regulatory Liabilities [Line Items]
Regulatory liabilities	471.1	0.0
Sentinel meter station depreciation
Regulatory Liabilities [Line Items]
Regulatory liabilities	6.3	6.2
Postretirement benefits other than pension
Regulatory Liabilities [Line Items]
Regulatory liabilities	73.9	63.0
Electric power cost
Regulatory Liabilities [Line Items]
Regulatory liabilities	13.3	6.3
Pension- deferred collections
Regulatory Liabilities [Line Items]
Regulatory liabilities	32.5	21.3
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.3	4.6
Grossed-up deferred taxes on equity funds used during construction
Regulatory Assets [Line Items]
Regulatory assets	37.9	73.2
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory assets	168.7	117.2
Asset retirement costs - Eminence
Regulatory Assets [Line Items]
Regulatory assets	49.5	53.9
Deferred taxes
Regulatory Assets [Line Items]
Regulatory assets	3.8	4.8
Deferred cash out
Regulatory Assets [Line Items]
Regulatory assets	42.5	48.2
Deferred gas costs
Regulatory Assets [Line Items]
Regulatory assets	6.0	0.0
Fuel Cost
Regulatory Assets [Line Items]
Regulatory assets	61.4	51.3
Other
Regulatory Assets [Line Items]
Regulatory assets	$ 3.7	$ 2.5

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Other (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Capitalization of project feasibility costs previously expensed	$ 0.2	$ 1.4