10-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

ý 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 1-7414

NORTHWEST PIPELINE LLC

(Exact name of registrant as specified in its charter)

DELAWARE	26-1157701
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)
295 Chipeta Way Salt Lake City, Utah	84108
(Address of principal executive offices)	(Zip Code)

Registrant’s telephone number, including area code: (801) 583-8800

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 Website, 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

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

NORTHWEST PIPELINE LLC

FORM 10-K

TABLE OF CONTENTS

	Page
PART I
Item 1. BUSINESS	3
Item 1A. RISK FACTORS	6
Item 1B. UNRESOLVED STAFF COMMENTS	16
Item 2. PROPERTIES	16
Item 3. LEGAL PROCEEDINGS	16
Item 4. MINE SAFETY DISCLOSURES	16
PART II
Item 5. MARKET FOR REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES	17
Item 6. SELECTED FINANCIAL DATA (Omitted)	17
Item 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS	17
Item 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK	20
Item 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA	21
Item 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE	42
Item 9A. CONTROLS AND PROCEDURES	42
Item 9B. OTHER INFORMATION	43
PART III
Item 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE (Omitted)	44
Item 11. EXECUTIVE COMPENSATION (Omitted)	44
Item 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS (Omitted)	44
Item 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE (Omitted)	44
Item 14. PRINCIPAL ACCOUNTING FEES AND SERVICES	44
PART IV
Item 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES	45
Item 16. FORM 10-K SUMMARY	47

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DEFINITIONS

We use the following gas measurements in this report:

Dth-means dekatherm.

Mdth-means thousand dekatherms.

MMdth-means million dekatherms.

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PART I

Item 1. BUSINESS

Northwest Pipeline LLC (Northwest) 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. Following these transactions, Williams owns a 74 percent limited partner interest in WPZ.

In this report, Northwest is at times referred to in the first person as “we,” “us,” or “our.”

GENERAL

We own and operate a natural gas pipeline system that extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through the states of Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington. We provide natural gas transportation services for markets in Washington, Oregon, Idaho, Wyoming, Nevada, Utah, Colorado, New Mexico, California and Arizona, either directly or indirectly through interconnections with other pipelines. Our principal business is the interstate transportation of natural gas, which is regulated by the Federal Energy Regulatory Commission (FERC).

Our system includes approximately 3,900 miles of mainline and lateral transmission pipeline and 41 transmission compressor stations. Our compression facilities have a combined sea level-rated capacity of approximately 472,000 horsepower. At December 31, 2017, we had long-term firm transportation contracts and storage redelivery agreements, with aggregate capacity reservations of approximately 3.8 MMdth of natural gas per day.

We own a one-third interest in the Jackson Prairie underground storage facility located near Chehalis, Washington. We have a contract with a third party under which we contract for natural gas storage services in an underground storage reservoir in the Clay Basin Field located in Daggett County, Utah. We also own and operate a Liquefied Natural Gas (LNG) storage facility near Plymouth, Washington. We have approximately 14.2 MMdth of working natural gas storage capacity through these three storage facilities, which is substantially utilized for third-party natural gas. These natural gas storage facilities enable us to balance daily receipts and deliveries and provide storage services to our customers.

We transport and store natural gas for a broad mix of customers, including local natural gas distribution companies, municipal utilities, direct industrial users, electric power generators, and natural gas marketers and producers. We offer firm and interruptible transportation and storage service. Our firm transportation and storage contracts are generally long-term contracts with various expiration dates and account for the major portion of our business. During 2017, our three largest customers were Puget Sound Energy, Inc., Northwest Natural Gas Company, and Cascade Natural Gas Corporation, which accounted for approximately 25.4 percent, 10.9 percent, and 10.2 percent, respectively, of our total operating revenues for the year ended December 31, 2017. No other customer accounted for more than 10 percent of our total operating revenues during that period.

Our rates are subject to the rate-making policies of the FERC. We provide a significant portion of our transportation and storage services pursuant to long-term firm contracts that obligate our customers to pay us monthly capacity reservation fees, which are fees that are owed for reserving an agreed upon amount of pipeline or storage capacity regardless of the amount of pipeline or storage capacity actually utilized by a customer. When a customer utilizes the capacity it has reserved under a firm transportation contract, we also collect a volumetric fee based on the quantity of natural gas transported. These volumetric fees are typically a small percentage of the total fees received under a firm contract. We also derive a small portion of our revenues from short-term firm and interruptible contracts under which customers pay fees for transportation, storage and other related services. The high percentage of our revenue derived from capacity reservation fees helps mitigate the risk of revenue fluctuations caused by changing supply and demand conditions.

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 volume and throughput assumptions. The

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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.

Our rates became effective January 1, 2018, and are expected to remain in effect for 5 years.

Rate Case Settlement Filing

On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with the Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file a general rate case to place new rates into effect after October 1, 2018, and that a general rate case must be filed for new rates to become effective no later than January 1, 2023.

Tax Reform Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its 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), among other things, reduces the corporate federal income tax rates. As part of our 2017 Settlement, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect.

Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. We recorded a regulatory liability for this difference. 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.

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 equipment and facilities resulting from storm events or natural disasters; and

• Blowouts, cratering, and explosions.

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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, and could exceed our expectations,” and “Item 8. Financial Statements and Supplementary Data – Notes to Financial Statements: Note 3. Contingent Liabilities and Commitments – Environmental Matters.”

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 along with periodic reassessments to be completed within required timeframes. In meeting the integrity regulations, we 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. 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

Northwest 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. Please see “Item 8. Financial Statements and Supplementary Data — Notes to Financial Statements: Note 1. Summary of Significant Accounting Policies” and “Note 7. Transactions with Major Customers and Affiliates.”

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Item 1A. RISK FACTORS

FORWARD-LOOKING STATEMENTS

The reports, filings, and other public announcements of Northwest Pipeline 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.

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;

• 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;

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

• 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;

• Uncontrolled releases of natural gas;

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• 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.

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.

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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.

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.

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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.

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

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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, Puget Sound Energy, Inc., accounted for approximately 25.4 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.

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.

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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.

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 $581.6 million.

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 make certain distributions during the continuation of an event of default and our ability 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 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.

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

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

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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 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 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.

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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.

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 is constructed and maintained on and across properties owned by others pursuant to rights-of-way, easements, permits, licenses or consents. Our compressor stations, with associated facilities, are located in whole or in part upon lands owned by us and upon sites held under leases or permits issued or approved by public authorities. Land owned by others, but used by us under rights-of-way, easements, permits, leases, licenses, or consents, includes land owned by private parties, federal, state, and local governments, quasi-governmental agencies, or Native American tribes. The Plymouth LNG facility is located on lands owned in fee simple by us. Various credit arrangements restrict the sale or disposal of a major portion of our pipeline system. We lease our company offices in Salt Lake City, Utah.

Item 3. LEGAL PROCEEDINGS

The information called for by this item is provided in “Item 8. Financial Statements and Supplementary Data – Notes to Financial Statements: Note 3. Contingent Liabilities and Commitments.”

Item 4. MINE SAFETY DISCLOSURES

Not applicable.

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PART II

Item 5. MARKET FOR REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

At December 31, 2017, we were indirectly owned by Williams Partners L.P., and Williams owned a 74 percent interest in Williams Partners L.P. 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. Following these transactions, Williams owns a 74 percent limited partner interest in WPZ.

We paid $186.0 million and $174.0 million in cash distributions during 2017 and 2016, respectively. During January 2018, we declared and paid cash distributions of $34.0 million to our parent.

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.

Item 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

GENERAL

The following discussion 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 “Part II, Item 8” of this report.

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 Topic (ASC) 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 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 Balance Sheet and included in the 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 amounts of regulatory assets reflected in the Balance Sheet are $27.5 million and $38.8 million at December 31, 2017 and 2016, respectively. The aggregate amounts of regulatory liabilities reflected in the Balance Sheet are $248.0 million and $32.2 million at December 31, 2017 and 2016, respectively.

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 collections of historical rates that reflected historical federal income tax rates, we expect we be required to return amounts to certain customers through future rates and have established a regulatory liability accordingly. This liability was recorded in December 2017 through a regulatory charge to operating income of $206.5 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.

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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 liabilities by approximately $13 million.

• 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.

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

Our regulatory assets associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $5.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net below Operating income.

A summary of regulatory assets and liabilities is included in Note 9 of Notes to Financial Statements.

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.

Our operating revenues decreased $0.6 million in 2017 as compared with 2016. This decrease is primarily associated with one less billable day of business in 2017, due to the 2016 leap year. Transportation service accounted for 97 percent and gas storage service accounted for 3 percent of our operating revenues for both 2017 and 2016.

Total operating expenses increased $209.4 million, or 82 percent, in 2017 as compared with 2016, due mainly to a $206.5 million regulatory charge associated with establishing a regulatory liability resulting from Tax Reform, a settlement charge from a pension early payout of $4.1 million, lower labor costs capitalized to projects of $2.5 million and increased charges for corporate administrative services of $2.2 million; partially offset by lower labor-related costs resulting from our workforce reductions that occurred in the first quarter 2016 of $3.0 million, a decrease in pipeline maintenance costs of $1.8 million which included a reduction in contractual, outside services and charges from affiliates and $1.6 million lower environmental expense.

Interest expense decreased $6.1 million, or 16 percent, in 2017 as compared with 2016 as a result of the retirement of our $175.0 million 7 percent senior unsecured notes that matured on June 15, 2016 and the retirement of the $185 million 5.95 percent notes in April 2017, partially offset by the interest expense recorded on the $250 million 4 percent senior unsecured notes issued on April 3, 2017.

Other income and expenses had an unfavorable change of $4.5 million in 2017 compared to 2016 primarily as a result of a regulatory charge as a result of Tax Reform reflecting a decrease in the regulatory asset associated with deferred taxes on equity AFUDC for periods when we were organized as a taxable entity.

The decrease in our net income is primarily due to the factors noted above.

Rate Case Settlement Filing

On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system

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firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file new rates to be effective after October 1, 2018, and that a general rate case filing must be made for rates to become effective no later than January 1, 2023. The Settlement is not expected to materially affect our trend of earnings.

Tax Reform Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its 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), among other things, reduces the corporate federal income tax rates. As part of our 2017 Settlement, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect.

Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. We recorded a regulatory liability for this difference. 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.

Effects of Inflation

We generally have 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 materials 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 made 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 future amounts raised, if any, in the capital markets. We anticipate that we will be able to access public and private debt markets on terms commensurate with our credit ratings to finance our capital requirements, when needed.

We, along with WPZ and Transcontinental Gas Pipe Line Company, LLC (Transco), 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 Transco.

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 $137.7 million. These advances are represented by demand notes.

Please see “Item 8. Financial Statements and Supplementary Data – Notes to Financial Statements: Note 4. Debt, Financing Arrangements, and Leases – Credit Facility and Note 7. Transactions with Major Customers and Affiliates – Related Party Transactions.”

19

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, obsolete, completing their useful life, or necessary to remain in compliance with environmental laws and regulations. Expansion capital expenditures improve the service capability of the 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 $82 million. Of this total, approximately $24 million is considered nondiscretionary due to legal, regulatory, and/or contractual requirements. In 2018, we expect to fund our capital expenditures with cash from operations.

Pipeline Projects

The North Seattle Lateral Upgrade (Project) involves an expanded delivery capabilities of Northwest’s North Seattle Lateral.  On May 11, 2017, we filed the FERC 7(c) application for the Project.  The Project consists of the removal and replacement of approximately 5.9 miles of 8-inch diameter pipeline with new 20-inch diameter pipeline.  We plan to place the Project into service as early as the fourth quarter of 2019, and it is expected to increase the delivery capacity by approximately 159 MDth/d.

Item 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Interest Rate Risk

Our interest rate risk exposure is limited to our long-term debt. All of our interest on long-term debt is fixed in nature as shown on the following table (in thousands of dollars):

	December 31, 2017
Fixed rates on long-term debt:
6.05% senior unsecured notes due 2018	$	250,000
7.125% unsecured debentures due 2025	85,000
4.0% unsecured debentures due 2027	250,000
	585,000
Unamortized debt issuance costs	(2,415		)
Unamortized debt discount	(963		)
Total long-term debt, including current portion	$	581,622

Our total long-term debt at December 31, 2017 had a carrying value of $581.6 million and a fair market value of $608.8 million. As of December 31, 2017, the weighted-average interest rate on our long-term debt was 5.33 percent.

20

Item 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

INDEX TO FINANCIAL STATEMENTS

	Page
Report of Independent Registered Public Accounting Firm	22
Statement of Comprehensive Income (Loss)	23
Balance Sheet	24
Statement of Member's Equity	26
Statement of Cash Flows	27
Notes to Financial Statements	28

21

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To The Management Committee and Member of Northwest Pipeline LLC

Opinion on the Financial Statements

We have audited the accompanying balance sheet of Northwest Pipeline LLC (the Company) as of December 31, 2017 and 2016, the related 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 “financial statements”). In our opinion, the 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 1986.

Houston, Texas

February 22, 2018

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NORTHWEST PIPELINE LLC

STATEMENT OF COMPREHENSIVE INCOME (LOSS)

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
OPERATING REVENUES	$	473,406		$	474,029		$	472,994
OPERATING EXPENSES:
General and administrative	54,512			52,343			57,105
Operation and maintenance	78,085			79,514			73,128
Depreciation and amortization	102,084			101,672			100,554
Regulatory debits	4,857			3,510			2,550
Taxes, other than income taxes	17,889			17,835			17,151
Regulatory charge resulting from Tax Reform (Note 1)	206,547			—			—
Other expenses, net	195			—			—
Total operating expenses	464,169			254,874			250,488
OPERATING INCOME	9,237			219,155			222,506
OTHER (INCOME) AND OTHER EXPENSES:
Interest expense	33,015			39,164			46,024
Allowance for equity and borrowed funds used during construction	(1,444		)	(1,371		)	(1,619		)
Miscellaneous other (income) expenses, net	5,500			907			(595		)
Total other (income) and other expenses	37,071			38,700			43,810
NET INCOME (LOSS)	(27,834		)	180,455			178,696
CASH FLOW HEDGES:
Amortization of cash flow hedges into Interest expense	—			(28		)	(62		)
COMPREHENSIVE INCOME (LOSS)	$	(27,834	)	$	180,427		$	178,634

See accompanying notes.

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NORTHWEST PIPELINE LLC

BALANCE SHEET

(Thousands of Dollars)

	December 31, 2017		December 31, 2016
ASSETS
CURRENT ASSETS:
Cash	$	—	$	—
Receivables:
Trade	38,884		42,702
Affiliated companies	1,921		1,321
Advances to affiliate	137,666		45,137
Other	2,618		598
Materials and supplies	10,084		10,106
Exchange gas due from others	2,720		3,869
Prepayments and other	6,423		5,740
Total current assets	200,316		109,473
PROPERTY, PLANT AND EQUIPMENT, at cost	3,396,776		3,319,516
Less-Accumulated depreciation	1,508,245		1,424,855
Total property, plant and equipment, net	1,888,531		1,894,661
OTHER ASSETS:
Deferred charges	934		2,122
Regulatory assets	22,747		34,900
Total other assets	23,681		37,022
Total assets	$	2,112,528	$	2,041,156

See accompanying notes.

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NORTHWEST PIPELINE LLC

BALANCE SHEET

(Thousands of Dollars)

	December 31, 2017		December 31, 2016
LIABILITIES AND MEMBER’S EQUITY
CURRENT LIABILITIES:
Payables:
Trade	$	11,053	$	11,243
Affiliated companies	11,298		7,293
Accrued liabilities:
Taxes, other than income taxes	11,617		11,435
Interest	3,677		3,501
Exchange gas due to others	4,500		4,169
Exchange gas offset	1,499		1,428
Customer advances	2,092		1,893
Other	6,655		5,224
Long-term debt due within one year	249,874		184,924
Total current liabilities	302,265		231,110
LONG-TERM DEBT	331,748		334,236
OTHER NONCURRENT LIABILITIES:
Asset retirement obligations	67,100		60,762
Regulatory liabilities	246,504		30,717
Other	1,730		7,316
Total other noncurrent liabilities	315,334		98,795
CONTINGENT LIABILITIES AND COMMITMENTS (Note 3)
MEMBER'S EQUITY:
Member’s capital	1,073,892		1,073,892
Retained earnings	89,289		303,123
Total member’s equity	1,163,181		1,377,015
Total liabilities and member’s equity	$	2,112,528	$	2,041,156

See accompanying notes.

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NORTHWEST PIPELINE LLC

STATEMENT OF MEMBER’S EQUITY

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
MEMBER'S CAPITAL:
Balance at beginning and end of period	$	1,073,892		$	1,073,892		$	1,073,892
RETAINED EARNINGS:
Balance at beginning of period	303,123			296,668			285,972
Net income (loss)	(27,834		)	180,455			178,696
Cash distributions to parent	(186,000		)	(174,000		)	(168,000		)
Balance at end of period	89,289			303,123			296,668
ACCUMULATED OTHER COMPREHENSIVE INCOME(LOSS):
Balance at beginning of period	—			28			90
Cash flow hedges:
Reclassification of unrecognized gain into earnings	—			(28		)	(62		)
Balance at end of period	—			—			28
Total member’s equity	$	1,163,181		$	1,377,015		$	1,370,588

See accompanying notes.

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NORTHWEST PIPELINE LLC

STATEMENT OF CASH FLOWS

(Thousands of Dollars)

	Years Ended December 31,
	2017			2016			2015
OPERATING ACTIVITIES:
Net income (Loss)	$	(27,834	)	$	180,455		$	178,696
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation	102,084			101,672			100,554
Regulatory debits	4,857			3,510			2,550
Regulatory charge resulting from Tax Reform (Note 1)	206,547			—			—
Amortization of deferred charges and credits	2,687			898			762
Allowance for equity funds used during construction	(1,104		)	(953		)	(1,099		)
Changes in current assets and liabilities:
Trade and other accounts receivable	1,798			845			(137		)
Affiliated receivables	(600		)	120			598
Exchange gas due from others	1,149			(1,617		)	7,349
Materials and supplies	22			77			(117		)
Other current assets	(687		)	424			(1,283		)
Trade accounts payable	271			(1,560		)	158
Affiliated payables	4,005			(4,666		)	(1,184		)
Exchange gas due to others	(1,149		)	1,617			(8,095		)
Other accrued liabilities	1,856			(2,089		)	5,410
Changes in noncurrent assets and liabilities:
Deferred charges	4,340			(7,275		)	(2,633		)
Regulatory liabilities	3,503			3,785			3,427
Noncurrent liabilities	(3,620		)	9,025			5,737
Net cash provided by operating activities	298,125			284,268			290,693
FINANCING ACTIVITIES:
Proceeds from long-term debt	249,102			—			—
Payments for debt issuance costs	(2,207		)	—			—
Retirement of long-term debt	(185,000		)	(175,000		)	—
Cash distributions to parent	(186,000		)	(174,000		)	(168,000		)
Net cash used in financing activities	(124,105		)	(349,000		)	(168,000		)
INVESTING ACTIVITIES:
Property, plant and equipment:
Capital expenditures, net of equity AFUDC*	(81,217		)	(80,383		)	(86,289		)
Contributions and advances for construction costs	872			1,308			1,499
Disposal of property, plant and equipment, net	(1,146		)	(1,280		)	(1,075		)
Advances to affiliates, net	(92,529		)	126,730			(36,813		)
Proceeds from insurance	—			18,188			—
Net cash provided by (used in) investing activities	(174,020		)	64,563			(122,678		)
NET (DECREASE) INCREASE IN CASH	—			(169		)	15
CASH AT BEGINNING OF PERIOD	—			169			154
CASH AT END OF PERIOD	$	—		$	—		$	169
____________________________________
* Increases to property, plant and equipment	$	(80,355	)	$	(72,432	)	$	(73,931	)
Changes in related accounts receivable, accounts payable, and accrued liabilities	(862		)	(7,951		)	(12,358		)
Capital expenditures, net of equity AFUDC	$	(81,217	)	$	(80,383	)	$	(86,289	)

See accompanying notes.

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Corporate Structure and Control

Northwest Pipeline LLC (Northwest) 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. Following these transactions, Williams owns a 74 percent limited partner interest in WPZ.

Northwest has no employees. Services are provided to Northwest by Williams and its affiliates. Northwest reimburses Williams and its affiliates for the costs of the employees including compensation and employee benefit plan costs and all related administrative costs.

In this report, Northwest is at times referred to in the first person as “we,” “us” or “our.”

Nature of Operations

We own and operate an interstate pipeline system for the mainline transmission of natural gas. This system extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington.

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, 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 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 customers through future rates of the future decrease in income taxes payable associated with Tax Reform. This liability was recorded in December 2017 through a regulatory charge to operating income of $206.5 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.

Our regulatory assets associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $5.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net below Operating income. (See Note 9 for further discussion.)

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the 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) litigation-related contingencies; 2) environmental remediation obligations; 3) impairment assessments of long-lived assets; 4) depreciation; and 5) asset retirement obligations 6) regulatory deferred tax.

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

Revenue Recognition

Our revenues are primarily from services pursuant to long term firm transportation and storage agreements. These agreements provide for a reservation charge based on the volume of contracted capacity and a volumetric charge based on the volume of gas delivered, both at rates specified in our FERC tariffs. We recognize revenues for reservation charges ratably over the contract period regardless of the volume of natural gas that is transported or stored. Revenues for volumetric charges, from both firm and interruptible transportation services and storage injection and withdrawal services, are recognized based on volumes of natural gas scheduled for delivery at the agreed upon delivery point or based on volumes of natural gas scheduled for injection or withdrawal from the storage facility.

In the course of providing transportation services to our customers, we may receive or deliver different quantities of gas from shippers than the quantities delivered or received on behalf of those shippers. These transactions result in imbalances, which are typically settled through the receipt or delivery of gas in the future. Customer imbalances to be repaid or recovered in-kind are recorded as exchange gas due from others or due to others in the accompanying balance sheets. The difference between exchange gas due to us from customers and the exchange gas that we owe to customers is included in the exchange gas offset. These imbalances are valued at the average of the spot market rates at the Canadian border and the Rocky Mountain market as published in the SNL Financial “Bidweek Index - Spot Rates.” 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.

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 third-party regulatory proceedings, advice of counsel and other risks. At December 31, 2017, we had no such rate refund liabilities.

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 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 (plant), consisting principally of natural gas transmission facilities, is recorded at original cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of plant are charged or credited 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 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
Storage Facilities	1.60	%	—	2.76%
Transmission Facilities	2.80	%	—	6.97%

The incrementally priced Evergreen Expansion Project, which was an expansion of our pipeline system, was placed in service on October 1, 2003. The levelized rate design of this project creates a consistent revenue stream over the related 25-year and 15-year customer contract terms. The related levelized depreciation is lower than book depreciation in the early years and higher than book depreciation in the later years of the contract terms. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The FERC has approved the accounting for the differences between book depreciation and the Evergreen Expansion Project’s levelized depreciation as a regulatory asset.

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

We recorded regulatory debits totaling $4.9 million in 2017, $3.5 million in 2016, and $2.6 million in 2015 in the accompanying Statement of Comprehensive Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Project discussed above.

We record a liability and increase the basis in the underlying asset for the present value of each expected future asset retirement obligation (ARO) at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of AROs includes, 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 market-risk premium. We measure changes in the liability due to passage of time by applying an interest rate to the liability balance. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2017 and 2016 were $82.2 million and $78.5 million, respectively. The regulatory asset is expected to be fully recovered through the net negative salvage component of depreciation included in our rates; as such, the negative salvage component of accumulated depreciation ($82.2 million and $78.5 million at December 31, 2017 and 2016, respectively) has been reclassified and netted against the amount of the ARO regulatory asset.

Impairment of Long-Lived Assets

We evaluate 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 such a determination has been made, our management’s estimate of undiscounted future cash flows attributable to the assets is compared to the carrying value of the assets to determine whether an impairment has occurred. If an impairment of the carrying value has occurred, the amount of the impairment recognized in the financial statements is determined by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

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. The use of alternate judgments and/or assumptions could result in the recognition of different levels of impairment charges in the financial statements.

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 is 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 $0.3 million for 2017, $0.4 million for 2016, and $0.5 million for 2015. The allowance for equity funds was $1.1 million, $1.0 million, and $1.1 million for 2017, 2016, and 2015, respectively. Both are reflected in Other (Income) and Other Expenses.

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.

Materials and Supplies Inventory

All inventories are stated at lower of cost or net realizable value. We determine the cost of the inventories using the average cost method.

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

We perform an annual review of materials and supplies inventories, including an 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.

Deferred Charges

We amortize deferred charges over varying periods consistent with the FERC approved accounting treatment and recovery for such deferred items. Unamortized debt expense, debt discount and losses on reacquired long-term debt are amortized by the bonds outstanding method over the related debt repayment periods.

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 5 for further discussion.) 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.

Interest Payments

Cash payments for interest, net of interest capitalized, were $31.9 million in 2017, $38.5 million in 2016, and $45.3 million in 2015.

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 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 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

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NOTES TO FINANCIAL STATEMENTS

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 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 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 the new standard 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. 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 systems and internal controls 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. RATE AND REGULATORY MATTERS

Rates

Our rates became effective January 1, 2018, and are expected to remain in effect for 5 years.

Rate Case Settlement Filing

On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with the Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file a general rate case to place new rates into effect after October 1, 2018, and that a general rate case must be filed for new rates to become effective no later than January 1, 2023.

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NOTES TO FINANCIAL STATEMENTS

Tax Reform Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its 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), among other things, reduces the corporate federal income tax rates. As part of our 2017 Settlement, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect.

Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. 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 the other costs of providing services. We recorded a regulatory liability for this difference.

3. CONTINGENT LIABILITIES AND COMMITMENTS

Environmental Matters

We are subject to the National Environmental Policy Act and other federal and state legislation regulating the environmental aspects of our business. Except as discussed below, our management believes that we are in substantial compliance with existing environmental requirements. Environmental expenditures are expensed or capitalized depending on their future economic benefit and potential for rate recovery. We believe that, with respect to any expenditures required to meet applicable standards and regulations, the Federal Energy Regulatory Commission (FERC) would grant the requisite rate relief so that substantially all of such expenditures would be permitted to be recovered through rates.

Beginning in the mid-1980s, we evaluated many of our facilities for the presence of toxic and hazardous substances to determine to what extent, if any, remediation might be necessary. We identified polychlorinated biphenyl (PCB) contamination in air compressor systems, soils, and related properties at certain compressor station sites. Similarly, we identified hydrocarbon impacts at these facilities due to the former use of earthen pits, lubricating oil leaks or spills, and excess pipe coating released to the environment. In addition, heavy metals have been identified at these sites due to the former use of mercury containing meters and paint and welding rods containing lead, cadmium, and arsenic. The PCBs were remediated pursuant to a Consent Decree with the U.S. Environmental Protection Agency (EPA) in the late 1980s, and we conducted a voluntary clean-up of the hydrocarbon and mercury impacts in the early 1990s. In 2005, the Washington Department of Ecology required us to re-evaluate our previous clean-ups in Washington. During 2006 to 2015, 129 meter stations were evaluated, of which 82 required remediation. As of December 31, 2017, all of the meter stations have been remediated. Initial assessments have been completed at all thirteen compressor stations in Washington. Additional assessments are ongoing at two of these compressor stations. Remediation has been completed at eleven of the thirteen compressor stations. On the basis of the findings to date, we estimate that environmental assessment and remediation costs will total approximately $3.0 million, measured on an undiscounted basis, and are expected to be incurred through 2022. At December 31, 2017 we had accrued liabilities totaling approximately $3.0 million, $1.3 million in current liabilities and $1.7 million in other noncurrent liabilities and at December 31, 2016 approximately $4.4 million, $1.3 million in current liabilities and $3.1 million in other noncurrent liabilities for these costs. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs.

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 Property, plant, and equipment - net in the 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.

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NOTES TO FINANCIAL STATEMENTS

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.

4. DEBT, FINANCING ARRANGEMENTS, AND LEASES

Long-Term Debt

Long-term debt, presented net of unamortized discount and unamortized debt issuance costs, consists of the following:

	December 31,
	2017			2016
	(Thousands of Dollars)
5.95% senior unsecured notes due 2017	$	—		$	185,000
6.05% senior unsecured notes due 2018	250,000			250,000
7.125% unsecured debentures due 2025	85,000			85,000
4.0% unsecured debentures due 2027	250,000			—
Debt issuance costs	(2,415		)	(624		)
Unamortized debt discount	(963		)	(216		)
Total long-term debt, including current portion	$	581,622		$	519,160
Long-term debt due within one year	249,874			184,924
Total long-term debt less current portion	$	331,748		$	334,236

As of December 31, 2017, cumulative maturities of outstanding long-term debt (at face value) for the next five years are as follows:

	(Thousands of Dollars)
2018: 6.05% senior unsecured notes	$	250,000
Total	$	250,000

There are no maturities applicable to long-term debt outstanding for the years 2019, 2020, 2021 and 2022.

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

The long-term debt due within one year at December 31, 2017 is associated with our $250 million 6.05% senior unsecured notes that mature on June 15, 2018. We intend to repay this maturing note by accessing available capacity under our revolving credit facility, advances from our parent, or issuing new long-term debt. The long-term debt due within one year at December 31, 2016 is associated with our $185 million 5.95% senior unsecured notes that matured on April 15, 2017.

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.

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NOTES TO FINANCIAL STATEMENTS

Issuance and Retirement of Long-Term Debt

On April 3, 2017, we issued $250 million of 4.0 percent senior unsecured notes due 2027 to investors in a private debt placement. We used the net proceeds to retire $185 million of 5.95 percent senior unsecured notes that matured on April 15, 2017, and for general corporate purposes. As part of the issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. Under the terms of the agreement, 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 of 1933, as amended, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. We have filed the registration statement, which became effective in January 2018. The exchange offer is expected to be completed in the first quarter of 2018.

Credit Facility

On February 2, 2015, we, along with WPZ, Transco, 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 an 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 anytime of $3 billion of unsecured commercial paper notes. At December 31, 2017, WPZ had no outstanding commercial paper.

Lease Obligations

Our leasing arrangements include mostly premise and equipment leases that are classified as operating leases.

Effective October 1, 2009, we entered into an agreement to lease office space from a third party. The agreement has an initial term of approximately 10 years, with an option to renew for an additional 5 or 10 year term.

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NOTES TO FINANCIAL STATEMENTS

Following are the estimated future minimum annual rental payments required under operating leases, which have initial or remaining noncancelable lease terms in excess of one year:

	(Thousands of Dollars)
2018	$	2,761
2019	2,787
Total	$	5,548

Operating lease rental expense, net of sublease revenues, amounted to $3.5 million, $2.7 million, and $2.7 million for 2017, 2016, and 2015, respectively.

5. 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. (See Note 7 for further discussion.)

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 $5.2 million in 2017, $2.3 million in 2016, and $4.4 million in 2015. Included in our 2017 pension costs is a $3.0 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 $1.1 million of allocated corporate expenses also associated with the settlement charge.

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 are eligible for subsidized retiree health care benefits. During 2017, 2016, and 2015, we received credits from Williams related to retiree health care and life insurance benefits of $3.5 million, $3.8 million and $3.4 million, respectively. These credits were recorded as regulatory liabilities.

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 difference between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities 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 $34.1 million and $30.6 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $2.1 million in 2017, $2.2 million in 2016, and $2.2 million in 2015 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 nonmanagement 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.

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NOTES TO FINANCIAL STATEMENTS

Total stock-based compensation expense for the years ended December 31, 2017, 2016 and 2015 was $1.9 million, $1.4 million and $1.5 million, respectively, excluding amounts allocated from WPZ and Williams.

6. FINANCIAL INSTRUMENTS

Fair Value of Financial Instruments

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:

Cash and advances to affiliate—The carrying amounts approximate fair value, because of the short-term nature of these instruments.

Long-term debt – The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined 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 carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.6 million and $608.8 million, respectively, at December 31, 2017, and $519.2 million and $546.8 million, respectively, at December 31, 2016.

7. TRANSACTIONS WITH MAJOR CUSTOMERS AND AFFILIATES

Concentration of Off-Balance-Sheet and Other Credit Risk

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Years Ended December 31,
	2017		2016		2015
	(Thousands of Dollars)
Puget Sound Energy, Inc.	$	120,226	$	120,351	$	118,384
Northwest Natural Gas Company	51,743		49,895		50,857
Cascade Natural Gas Corporation	48,071		47,951		48,363

Our major customers are located in the Pacific Northwest. As a general policy, collateral is not required for receivables, but customers’ financial condition and credit worthiness are regularly evaluated and historical collection losses have been minimal.

Related Party Transactions

We are a participant in WPZ’s cash management program. At December 31, 2017 and 2016, the advances due to us by WPZ totaled approximately $137.7 million and $45.1 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to Affiliates in the accompanying Balance Sheet. 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, which was approximately 1.16 percent at December 31, 2017. The interest income from these advances was minimal during the years ended December 31, 2017, 2016, and 2015. Such interest income is included in Other (Income) and Other Expenses: Miscellaneous other (income) expenses, net on the accompanying Statement of Comprehensive Income.

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 $96.5 million, $92.8 million, and $100.4 million in the years ended December 31, 2017, 2016, and 2015, respectively, for these services. Such expenses are primarily included in General and administrative and Operation and maintenance expenses on the accompanying Statement of Comprehensive Income. The

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NOTES TO FINANCIAL STATEMENTS

amount billed to us during 2016 includes $2.4 million for severance and other related costs associated with a reduction in workforce primarily recognized in the first quarter.

During 2017, 2016, and 2015, we declared and paid cash distributions to our parent of $186.0 million, $174.0 million, and $168.0 million, respectively. During January 2018, we declared and paid cash distributions of $34.0 million to our parent.

8. ASSET RETIREMENT OBLIGATIONS

Our accrued asset retirement obligations relate to our gas storage and transmission facilities. At the end of the useful life of our facilities, we are legally obligated to remove or plug and abandon certain transmission facilities including underground pipelines, major river spans, compressor stations and meter station facilities. These obligations also include restoration of the property sites after removal of the facilities from above and below the ground.

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

	2017			2016
Beginning balance	$	60,762		$	82,454
Accretion	3,968			7,470
New obligations	149			150
Changes in estimates of existing obligations (1)	2,510			(29,312		)
Property dispositions/obligations settled	(289		)	—
Ending balance	$	67,100		$	60,762

(1) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rates, current estimates for removal cost, the estimated remaining life of assets, and discount rates. The increase in 2017 is primarily attributed to an increase in the inflation rate and a decrease in the estimated useful life of the assets. The decrease in 2016 is primarily attributed to decreases in current estimates for removal costs and inflation rate and an increase in the estimated life of the assets.

9. REGULATORY ASSETS AND LIABILITIES

Our regulatory assets and liabilities result from our application of the provisions of Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Exchange gas offset and Prepayments and other. Current regulatory liabilities are included in Exchange gas offset. These balances are presented on our Balance Sheet on a gross basis and are recoverable or refundable over various periods. Below are the details of our regulatory assets and liabilities as of December 31, 2017 and 2016:

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NOTES TO FINANCIAL STATEMENTS

	2017		2016
	(Thousands of Dollars)
Current regulatory assets:
Levelized depreciation	$	4,707	$	3,864
Total current regulatory assets	4,707		3,864
Noncurrent regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	6,598		13,051
Levelized depreciation	16,149		21,849
Total noncurrent regulatory assets	22,747		34,900
Total regulatory assets	$	27,454	$	38,764
Current regulatory liabilities:
Fuel recovery	$	1,539	$	1,466
Noncurrent regulatory liabilities:
Postretirement benefits	34,089		30,587
Deferred taxes-liability	206,547		—
Asset retirement obligations, net	5,868		130
Total noncurrent regulatory liabilities	246,504		30,717
Total regulatory liabilities	$	248,043	$	32,183

The significant regulatory assets and liabilities include:

Levelized Depreciation Levelized depreciation allows contract revenue streams to remain constant over the primary contract terms by recognizing lower than book depreciation in the early years and higher than book depreciation in later years. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The difference between levelized depreciation and straight-line book depreciation is recorded as a FERC approved regulatory asset or liability and is eliminated over the levelization period.

Grossed-Up Deferred Taxes on Equity Funds Used During Construction The regulatory asset balance was 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, net This regulatory liability balance reflects the amount that we have recovered in our rates related to our future retirement costs offset by depreciation of the ARO asset and changes in the ARO liability due to the passage of time. ARO’s are expected to be fully recovered through the net negative salvage component of depreciation included in our rates. (See Note 8 for further discussion)

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.(See Note 1). In addition to this amount, as part of our 2017 rate case settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates changed due to subsequent legislation, such as the recently enacted Tax Reform, we would record a regulatory liability. As a result of Tax Reform, the regulatory liability will be $23.6 million annually for the period beginning January 1, 2018 and continuing through the time that our current rates remain effective.

Fuel Recovery These amounts reflect the value of the cumulative volumetric 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 or refunded by changing the fuel reimbursement factor in subsequent fuel filings.

Postretirement Benefits We seek to recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any differences between the annual actuarially determined cost and amounts currently

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NOTES TO FINANCIAL STATEMENTS

being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. These amounts are not included in the rate base, and we are not currently recovering postretirement benefit costs in our rates. (See Note 5)

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QUARTERLY FINANCIAL DATA

(Unaudited)

The following is a summary of unaudited quarterly financial data for 2017 and 2016:

	Quarter of 2017
	First		Second		Third		Fourth (1)
	(Thousands of Dollars)
Operating revenues	$	120,500	$	115,094	$	116,188	$	121,624
Operating income (loss)	59,478		51,816		51,584		(153,641		)
Net income (loss)	51,149		43,632		44,062		(166,677		)

	Quarter of 2016
	First		Second		Third		Fourth
	(Thousands of Dollars)
Operating revenues	$	120,448	$	115,569	$	116,897	$	121,115
Operating income	58,853		50,703		53,356		56,243
Net income	47,121		39,962		45,258		48,114

(1) Includes $206.5 million regulatory charge resulting from Tax Reform. Includes $4.1 million increase to operating expenses for a Pension Plan Settlement adjustment. Includes $5.7 million unfavorable change to other (income) and deductions, net for a reduction in the tax gross-up on equity AFUDC due to the tax rate change.

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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 — West and our Vice President 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 — West and our Vice President and Chief Accounting Officer. Based upon that evaluation, our Senior Vice President — West and our Vice President 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.

Under the supervision and with the participation of our management, including our Senior Vice President — West and our Vice President 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.

42

This annual report does not include a report of our registered public accounting firm regarding internal control over financial reporting. A report by our 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.

43

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.

Item 14. PRINCIPAL ACCOUNTING FEES AND SERVICES

Fees for professional services provided by our independent auditors in each of the last two fiscal years in each of the following categories are:

	2017		2016
	(Thousands of Dollars)
Audit fees	$	700	$	637
Audit related fees	—		—
Tax fees	—		—
All other fees	—		—
	$	700	$	637

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 consultations.

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 at http://investor.williams.com.

44

PART IV

Item 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

	Page Reference to 2017 Form 10-K
(a) 1. and 2. Northwest Pipeline LLC financials
Index
Covered by reports of independent auditors:
Statement of Comprehensive Income (Loss) for the Years Ended December 31, 2017, 2016, and 2015	23
Balance Sheet at December 31, 2017 and 2016	24
Statement of Member’s Equity for the Years Ended December 31, 2017, 2016, and 2015	26
Statement of Cash Flows for the Years Ended December 31, 2017, 2016, and 2015	27
Notes to Financial Statements	28
Not covered by reports of independent auditors:
Quarterly Financial Data (Unaudited)	41

All other schedules have been omitted since the required information is not present or is not present in amounts sufficient to require submission of the schedule, or because the information required is included in the financial statements and notes thereto.

45

(a) 3 and b. Exhibits:

Exhibit	Description
2	Certificate of Conversion of Northwest Pipeline GP (filed on July 3, 2013 as Exhibit 2.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
3.1	Certificate of Formation of Northwest Pipeline LLC (filed on July 3, 2013 as Exhibit 2.2 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
3.2	Operating Agreement of Northwest Pipeline LLC (filed on July 3, 2013 as Exhibit 3.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
4.1	Senior Indenture, dated as of November 30, 1995 between Northwest Pipeline Corporation and Chemical Bank, relating to Northwest Pipeline’s 7.125% Debentures due 2025 (filed on September 14, 1995 as Exhibit 4.1 to our registration statement on Form S-3 (File No. 033-62639) and incorporated herein by reference).
4.2	Indenture, dated May 22, 2008, between Northwest Pipeline GP and The Bank of New York Trust Company, N.A., as trustee, relating to $250 million aggregate principal amount of 6.05% Senior Notes due 2018 (filed on May 23, 2008 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
4.3	Indenture, dated as of April 3, 2017, between Northwest Pipeline LLC and The Bank of New York Mellon Trust Company, N.A., as trustee (filed on April 3, 2017 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
10.1	Administrative Services Agreement, dated January 24, 2008, between Northwest Pipeline GP and Northwest Pipeline Services LLC (filed on January 30, 2008 as Exhibit 10.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
10.2	Assignment Agreement dated February 13, 2013, by and between Northwest Pipeline Services LLC and Williams WPC-I, LLC, effective January 1, 2013 (filed on February 3, 2015 as Exhibit 10(b) to our annual report on Form 10-K (File No. 001-07414) 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, and 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 report on Form 8-K (File No. 001-07414) 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).
10.6	Registration Rights Agreement, dated April 3, 2017, between Northwest Pipeline LLC and the initial purchasers listed therein (filed on April 3, 2017 as Exhibit 10.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
23.1*	Consent of Ernst & Young LLP.
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.
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*	XBRL Instance Document.
101.SCH*	XBRL Taxonomy Extension Schema.
101.CAL*	XBRL Taxonomy Extension Calculation Linkbase.

46

101.DEF*	XBRL Taxonomy Definition Linkbase
101.LAB*	XBRL Taxonomy Extension Label Linkbase.
101.PRE*	XBRL Taxonomy Extension Presentation Linkbase.

* Filed herewith

** Furnished herewith

Item 16. FORM 10-K SUMMARY

Not applicable.

47

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.

NORTHWEST PIPELINE 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 in the capacities and on the dates indicated.

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

Date: February 22, 2018

EX-23

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement (Form S-4 No. 333-222633) of Northwest Pipeline LLC and in the related Prospectus of our report dated February 22, 2018, with respect to the financial statements of Northwest Pipeline LLC included in this Annual Report (Form 10-K) for the year ended December 31, 2017.

/s/ Ernst & Young LLP

Houston, Texas

February 22, 2018

EX-31.1

Exhibit 31.1

SECTION 302 CERTIFICATION

I, Walter J. Bennett, certify that:

1. I have reviewed this annual report on Form 10-K of Northwest Pipeline 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/ Walter J. Bennett
	Walter J. Bennett
	Sr. Vice President—West
	(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 Northwest Pipeline 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 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 Northwest Pipeline 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/ Walter J. Bennett

Walter J. Bennett

Senior Vice President—West

February 22, 2018

/s/ Ted T. Timmermans

Ted T. Timmermans

Vice President 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 - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 22, 2018
Entity Information [Line Items]
Entity Registrant Name	Northwest Pipeline LLC
Entity Central Index Key	0000110019
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

Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING REVENUES	$ 473,406	$ 474,029	$ 472,994
OPERATING EXPENSES:
General and administrative	54,512	52,343	57,105
Operation and maintenance	78,085	79,514	73,128
Depreciation and amortization	102,084	101,672	100,554
Regulatory debits	4,857	3,510	2,550
Taxes, other than income taxes	17,889	17,835	17,151
Regulatory charge resulting from Tax Reform (Note 1)	206,547	0	0
Other expenses, net	195	0	0
Total operating expenses	464,169	254,874	250,488
OPERATING INCOME	9,237	219,155	222,506
OTHER (INCOME) AND OTHER EXPENSES:
Interest expense	33,015	39,164	46,024
Allowance for equity and borrowed funds used during construction	(1,444)	(1,371)	(1,619)
Miscellaneous other (income) expenses, net	5,500	907	(595)
Total other (income) and other expenses	37,071	38,700	43,810
NET INCOME (LOSS)	(27,834)	180,455	178,696
CASH FLOW HEDGES:
Amortization of cash flow hedges into Interest expense	0	(28)	(62)
COMPREHENSIVE INCOME (LOSS)	$ (27,834)	$ 180,427	$ 178,634

XML

Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS:
Cash	$ 0	$ 0
Receivables:
Trade	38,884	42,702
Affiliated companies	1,921	1,321
Advances to affiliate	137,666	45,137
Other	2,618	598
Materials and supplies	10,084	10,106
Exchange gas due from others	2,720	3,869
Prepayments and other	6,423	5,740
Total current assets	200,316	109,473
PROPERTY, PLANT AND EQUIPMENT, at cost	3,396,776	3,319,516
Less-Accumulated depreciation	1,508,245	1,424,855
Total property, plant and equipment, net	1,888,531	1,894,661
OTHER ASSETS:
Deferred charges	934	2,122
Regulatory assets	22,747	34,900
Total other assets	23,681	37,022
Total assets	2,112,528	2,041,156
Payables:
Trade	11,053	11,243
Affiliated companies	11,298	7,293
Accrued liabilities:
Taxes, other than income taxes	11,617	11,435
Interest	3,677	3,501
Exchange gas due to others	4,500	4,169
Exchange gas offset	1,499	1,428
Customer advances	2,092	1,893
Other	6,655	5,224
Long-term debt due within one year	249,874	184,924
Total current liabilities	302,265	231,110
LONG-TERM DEBT	331,748	334,236
OTHER NONCURRENT LIABILITIES:
Asset retirement obligations	67,100	60,762
Regulatory liabilities	246,504	30,717
Other	1,730	7,316
Total other noncurrent liabilities	315,334	98,795
CONTINGENT LIABILITIES AND COMMITMENTS (Note 3)
MEMBER'S EQUITY:
Member's capital	1,073,892	1,073,892
Retained earnings	89,289	303,123
Total member's equity	1,163,181	1,377,015
Total liabilities and member's equity	$ 2,112,528	$ 2,041,156

XML

Statement of Member's Equity Statement of Member's Equity - USD ($) $ in Thousands	Total	MEMBER'S CAPITAL	RETAINED EARINGS	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
Balance at beginning of period at Dec. 31, 2014		$ 1,073,892	$ 285,972	$ 90
Net income (loss)	$ 178,696		178,696
Cash distributions to parent	(168,000)		(168,000)
Reclassification of unrecognized gain into earnings	(62)			(62)
Balance at end of period at Dec. 31, 2015	1,370,588	1,073,892	296,668	28
Net income (loss)	180,455		180,455
Cash distributions to parent	(174,000)		(174,000)
Reclassification of unrecognized gain into earnings	(28)			(28)
Balance at end of period at Dec. 31, 2016	1,377,015	$ 1,073,892	303,123	0
Net income (loss)	(27,834)		(27,834)
Cash distributions to parent	(186,000)		(186,000)
Reclassification of unrecognized gain into earnings	0			0
Balance at end of period at Dec. 31, 2017	$ 1,163,181		$ 89,289	$ 0

XML

Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net income (loss)	$ (27,834)	$ 180,455	$ 178,696
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation	102,084	101,672	100,554
Regulatory debits	4,857	3,510	2,550
Regulatory charge resulting from Tax Reform (Note 1)	206,547	0	0
Amortization of deferred charges and credits	2,687	898	762
Allowance for equity funds used during construction	(1,104)	(953)	(1,099)
Changes in current assets and liabilities:
Trade and other accounts receivable	1,798	845	(137)
Affiliated receivables	(600)	120	598
Exchange gas due from others	1,149	(1,617)	7,349
Materials and supplies	22	77	(117)
Other current assets	(687)	424	(1,283)
Trade accounts payable	271	(1,560)	158
Affiliated payables	4,005	(4,666)	(1,184)
Exchange gas due to others	(1,149)	1,617	(8,095)
Other accrued liabilities	1,856	(2,089)	5,410
Changes in noncurrent assets and liabilities:
Deferred charges	4,340	(7,275)	(2,633)
Regulatory liabilities	3,503	3,785	3,427
Noncurrent liabilities	(3,620)	9,025	5,737
Net cash provided by operating activities	298,125	284,268	290,693
FINANCING ACTIVITIES:
Proceeds from long-term debt	249,102	0	0
Payments for debt issuance costs	2,207	0	0
Retirement of long-term debt	(185,000)	(175,000)	0
Cash distributions to parent	(186,000)	(174,000)	(168,000)
Net cash used in financing activities	(124,105)	(349,000)	(168,000)
Property, plant and equipment:
Capital expenditures, net of equity AFUDC	(81,217)	(80,383)	(86,289)
Contributions and Advances for Construction Costs	872	1,308	1,499
Disposal of property, plant and equipment, net	(1,146)	(1,280)	(1,075)
Advances to affiliates, net	(92,529)	126,730	(36,813)
Proceeds from insurance	0	18,188	0
Net cash provided by (used in) investing activities	(174,020)	64,563	(122,678)
NET (DECREASE) INCREASE IN CASH	0	(169)	15
CASH AT BEGINNING OF PERIOD	0	169	154
CASH AT END OF PERIOD	0	0	169
Supplemental Cash Flow Elements [Abstract]
Increases to property, plant and equipment	(80,355)	(72,432)	(73,931)
Changes in related accounts receivable, accounts payable, and accrued liabilities	(862)	(7,951)	(12,358)
Capital expenditures, net of equity AFUDC	$ (81,217)	$ (80,383)	$ (86,289)

XML

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

Northwest Pipeline LLC (Northwest) 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. Following these transactions, Williams owns a 74 percent limited partner interest in WPZ.

Northwest has no employees. Services are provided to Northwest by Williams and its affiliates. Northwest reimburses Williams and its affiliates for the costs of the employees including compensation and employee benefit plan costs and all related administrative costs.

In this report, Northwest is at times referred to in the first person as “we,” “us” or “our.”

Nature of Operations

We own and operate an interstate pipeline system for the mainline transmission of natural gas. This system extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington.

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, 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 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 customers through future rates of the future decrease in income taxes payable associated with Tax Reform. This liability was recorded in December 2017 through a regulatory charge to operating income of $206.5 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.

Our regulatory assets associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $5.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net below Operating income. (See Note 9 for further discussion.)

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the 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) litigation-related contingencies; 2) environmental remediation obligations; 3) impairment assessments of long-lived assets; 4) depreciation; and 5) asset retirement obligations 6) regulatory deferred tax.

Revenue Recognition

Our revenues are primarily from services pursuant to long term firm transportation and storage agreements. These agreements provide for a reservation charge based on the volume of contracted capacity and a volumetric charge based on the volume of gas delivered, both at rates specified in our FERC tariffs. We recognize revenues for reservation charges ratably over the contract period regardless of the volume of natural gas that is transported or stored. Revenues for volumetric charges, from both firm and interruptible transportation services and storage injection and withdrawal services, are recognized based on volumes of natural gas scheduled for delivery at the agreed upon delivery point or based on volumes of natural gas scheduled for injection or withdrawal from the storage facility.

In the course of providing transportation services to our customers, we may receive or deliver different quantities of gas from shippers than the quantities delivered or received on behalf of those shippers. These transactions result in imbalances, which are typically settled through the receipt or delivery of gas in the future. Customer imbalances to be repaid or recovered in-kind are recorded as exchange gas due from others or due to others in the accompanying balance sheets. The difference between exchange gas due to us from customers and the exchange gas that we owe to customers is included in the exchange gas offset. These imbalances are valued at the average of the spot market rates at the Canadian border and the Rocky Mountain market as published in the SNL Financial “Bidweek Index - Spot Rates.” 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.

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 third-party regulatory proceedings, advice of counsel and other risks. At December 31, 2017, we had no such rate refund liabilities.

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 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 (plant), consisting principally of natural gas transmission facilities, is recorded at original cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of plant are charged or credited 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 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
Storage Facilities	1.60	%	—	2.76%
Transmission Facilities	2.80	%	—	6.97%

The incrementally priced Evergreen Expansion Project, which was an expansion of our pipeline system, was placed in service on October 1, 2003. The levelized rate design of this project creates a consistent revenue stream over the related 25-year and 15-year customer contract terms. The related levelized depreciation is lower than book depreciation in the early years and higher than book depreciation in the later years of the contract terms. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The FERC has approved the accounting for the differences between book depreciation and the Evergreen Expansion Project’s levelized depreciation as a regulatory asset.

We recorded regulatory debits totaling $4.9 million in 2017, $3.5 million in 2016, and $2.6 million in 2015 in the accompanying Statement of Comprehensive Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Project discussed above.

We record a liability and increase the basis in the underlying asset for the present value of each expected future asset retirement obligation (ARO) at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of AROs includes, 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 market-risk premium. We measure changes in the liability due to passage of time by applying an interest rate to the liability balance. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2017 and 2016 were $82.2 million and $78.5 million, respectively. The regulatory asset is expected to be fully recovered through the net negative salvage component of depreciation included in our rates; as such, the negative salvage component of accumulated depreciation ($82.2 million and $78.5 million at December 31, 2017 and 2016, respectively) has been reclassified and netted against the amount of the ARO regulatory asset.

Impairment of Long-Lived Assets

We evaluate 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 such a determination has been made, our management’s estimate of undiscounted future cash flows attributable to the assets is compared to the carrying value of the assets to determine whether an impairment has occurred. If an impairment of the carrying value has occurred, the amount of the impairment recognized in the financial statements is determined by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

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. The use of alternate judgments and/or assumptions could result in the recognition of different levels of impairment charges in the financial statements.

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 is 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 $0.3 million for 2017, $0.4 million for 2016, and $0.5 million for 2015. The allowance for equity funds was $1.1 million, $1.0 million, and $1.1 million for 2017, 2016, and 2015, respectively. Both are reflected in Other (Income) and Other Expenses.

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.

Materials and Supplies Inventory

All inventories are stated at lower of cost or net realizable value. We determine the cost of the inventories using the average cost method.

We perform an annual review of materials and supplies inventories, including an 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.

Deferred Charges

We amortize deferred charges over varying periods consistent with the FERC approved accounting treatment and recovery for such deferred items. Unamortized debt expense, debt discount and losses on reacquired long-term debt are amortized by the bonds outstanding method over the related debt repayment periods.

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 5 for further discussion.) 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.

Interest Payments

Cash payments for interest, net of interest capitalized, were $31.9 million in 2017, $38.5 million in 2016, and $45.3 million in 2015.

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 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 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 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 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 the new standard 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. 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 systems and internal controls 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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Rate and Regulatory Matters (Notes)

12 Months Ended

Dec. 31, 2017

Public Utilities, Rate Matters [Abstract]

Public Utilities, Disclosure of Rate Matters [Text Block]

RATE AND REGULATORY MATTERS

Rates

Our rates became effective January 1, 2018, and are expected to remain in effect for 5 years.

Rate Case Settlement Filing

On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with the Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file a general rate case to place new rates into effect after October 1, 2018, and that a general rate case must be filed for new rates to become effective no later than January 1, 2023.

Tax Reform Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its 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), among other things, reduces the corporate federal income tax rates. As part of our 2017 Settlement, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect.

Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. 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 the other costs of providing services. We recorded a regulatory liability for this difference.

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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

Environmental Matters

We are subject to the National Environmental Policy Act and other federal and state legislation regulating the environmental aspects of our business. Except as discussed below, our management believes that we are in substantial compliance with existing environmental requirements. Environmental expenditures are expensed or capitalized depending on their future economic benefit and potential for rate recovery. We believe that, with respect to any expenditures required to meet applicable standards and regulations, the Federal Energy Regulatory Commission (FERC) would grant the requisite rate relief so that substantially all of such expenditures would be permitted to be recovered through rates.

Beginning in the mid-1980s, we evaluated many of our facilities for the presence of toxic and hazardous substances to determine to what extent, if any, remediation might be necessary. We identified polychlorinated biphenyl (PCB) contamination in air compressor systems, soils, and related properties at certain compressor station sites. Similarly, we identified hydrocarbon impacts at these facilities due to the former use of earthen pits, lubricating oil leaks or spills, and excess pipe coating released to the environment. In addition, heavy metals have been identified at these sites due to the former use of mercury containing meters and paint and welding rods containing lead, cadmium, and arsenic. The PCBs were remediated pursuant to a Consent Decree with the U.S. Environmental Protection Agency (EPA) in the late 1980s, and we conducted a voluntary clean-up of the hydrocarbon and mercury impacts in the early 1990s. In 2005, the Washington Department of Ecology required us to re-evaluate our previous clean-ups in Washington. During 2006 to 2015, 129 meter stations were evaluated, of which 82 required remediation. As of December 31, 2017, all of the meter stations have been remediated. Initial assessments have been completed at all thirteen compressor stations in Washington. Additional assessments are ongoing at two of these compressor stations. Remediation has been completed at eleven of the thirteen compressor stations. On the basis of the findings to date, we estimate that environmental assessment and remediation costs will total approximately $3.0 million, measured on an undiscounted basis, and are expected to be incurred through 2022. At December 31, 2017 we had accrued liabilities totaling approximately $3.0 million, $1.3 million in current liabilities and $1.7 million in other noncurrent liabilities and at December 31, 2016 approximately $4.4 million, $1.3 million in current liabilities and $3.1 million in other noncurrent liabilities for these costs. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs.

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 Property, plant, and equipment - net in the 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.

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.

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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

Long-term debt, presented net of unamortized discount and unamortized debt issuance costs, consists of the following:

	December 31,
	2017			2016
	(Thousands of Dollars)
5.95% senior unsecured notes due 2017	$	—		$	185,000
6.05% senior unsecured notes due 2018	250,000			250,000
7.125% unsecured debentures due 2025	85,000			85,000
4.0% unsecured debentures due 2027	250,000			—
Debt issuance costs	(2,415		)	(624		)
Unamortized debt discount	(963		)	(216		)
Total long-term debt, including current portion	$	581,622		$	519,160
Long-term debt due within one year	249,874			184,924
Total long-term debt less current portion	$	331,748		$	334,236

As of December 31, 2017, cumulative maturities of outstanding long-term debt (at face value) for the next five years are as follows:

	(Thousands of Dollars)
2018: 6.05% senior unsecured notes	$	250,000
Total	$	250,000

There are no maturities applicable to long-term debt outstanding for the years 2019, 2020, 2021 and 2022.

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

The long-term debt due within one year at December 31, 2017 is associated with our $250 million 6.05% senior unsecured notes that mature on June 15, 2018. We intend to repay this maturing note by accessing available capacity under our revolving credit facility, advances from our parent, or issuing new long-term debt. The long-term debt due within one year at December 31, 2016 is associated with our $185 million 5.95% senior unsecured notes that matured on April 15, 2017.

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.

Issuance and Retirement of Long-Term Debt

On April 3, 2017, we issued $250 million of 4.0 percent senior unsecured notes due 2027 to investors in a private debt placement. We used the net proceeds to retire $185 million of 5.95 percent senior unsecured notes that matured on April 15, 2017, and for general corporate purposes. As part of the issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. Under the terms of the agreement, 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 of 1933, as amended, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. We have filed the registration statement, which became effective in January 2018. The exchange offer is expected to be completed in the first quarter of 2018.

Credit Facility

On February 2, 2015, we, along with WPZ, Transco, 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 an 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 anytime of $3 billion of unsecured commercial paper notes. At December 31, 2017, WPZ had no outstanding commercial paper.

Lease Obligations

Our leasing arrangements include mostly premise and equipment leases that are classified as operating leases.

Effective October 1, 2009, we entered into an agreement to lease office space from a third party. The agreement has an initial term of approximately 10 years, with an option to renew for an additional 5 or 10 year term.

Following are the estimated future minimum annual rental payments required under operating leases, which have initial or remaining noncancelable lease terms in excess of one year:

	(Thousands of Dollars)
2018	$	2,761
2019	2,787
Total	$	5,548

Operating lease rental expense, net of sublease revenues, amounted to $3.5 million, $2.7 million, and $2.7 million for 2017, 2016, and 2015, respectively.

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Benefit Plans (Notes)

12 Months Ended

Dec. 31, 2017

Disclosure Text Block [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. (See Note 7 for further discussion.)

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 $5.2 million in 2017, $2.3 million in 2016, and $4.4 million in 2015. Included in our 2017 pension costs is a $3.0 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 $1.1 million of allocated corporate expenses also associated with the settlement charge.

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 are eligible for subsidized retiree health care benefits. During 2017, 2016, and 2015, we received credits from Williams related to retiree health care and life insurance benefits of $3.5 million, $3.8 million and $3.4 million, respectively. These credits were recorded as regulatory liabilities.

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 difference between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities 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 $34.1 million and $30.6 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $2.1 million in 2017, $2.2 million in 2016, and $2.2 million in 2015 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 nonmanagement 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 $1.9 million, $1.4 million and $1.5 million, respectively, excluding amounts allocated from WPZ and Williams.

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Financial Instruments (Notes)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Financial Instruments

FINANCIAL INSTRUMENTS

Fair Value of Financial Instruments

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:

Cash and advances to affiliate—The carrying amounts approximate fair value, because of the short-term nature of these instruments.

Long-term debt – The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined 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 carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.6 million and $608.8 million, respectively, at December 31, 2017, and $519.2 million and $546.8 million, respectively, at December 31, 2016.

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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

Concentration of Off-Balance-Sheet and Other Credit Risk

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Years Ended December 31,
	2017		2016		2015
	(Thousands of Dollars)
Puget Sound Energy, Inc.	$	120,226	$	120,351	$	118,384
Northwest Natural Gas Company	51,743		49,895		50,857
Cascade Natural Gas Corporation	48,071		47,951		48,363

Our major customers are located in the Pacific Northwest. As a general policy, collateral is not required for receivables, but customers’ financial condition and credit worthiness are regularly evaluated and historical collection losses have been minimal.

Related Party Transactions

We are a participant in WPZ’s cash management program. At December 31, 2017 and 2016, the advances due to us by WPZ totaled approximately $137.7 million and $45.1 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to Affiliates in the accompanying Balance Sheet. 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, which was approximately 1.16 percent at December 31, 2017. The interest income from these advances was minimal during the years ended December 31, 2017, 2016, and 2015. Such interest income is included in Other (Income) and Other Expenses: Miscellaneous other (income) expenses, net on the accompanying Statement of Comprehensive Income.

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 $96.5 million, $92.8 million, and $100.4 million in the years ended December 31, 2017, 2016, and 2015, respectively, for these services. Such expenses are primarily included in General and administrative and Operation and maintenance expenses on the accompanying Statement of Comprehensive Income. The amount billed to us during 2016 includes $2.4 million for severance and other related costs associated with a reduction in workforce primarily recognized in the first quarter.

During 2017, 2016, and 2015, we declared and paid cash distributions to our parent of $186.0 million, $174.0 million, and $168.0 million, respectively. During January 2018, we declared and paid cash distributions of $34.0 million to our parent.

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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

Our accrued asset retirement obligations relate to our gas storage and transmission facilities. At the end of the useful life of our facilities, we are legally obligated to remove or plug and abandon certain transmission facilities including underground pipelines, major river spans, compressor stations and meter station facilities. These obligations also include restoration of the property sites after removal of the facilities from above and below the ground.

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

	2017			2016
Beginning balance	$	60,762		$	82,454
Accretion	3,968			7,470
New obligations	149			150
Changes in estimates of existing obligations (1)	2,510			(29,312		)
Property dispositions/obligations settled	(289		)	—
Ending balance	$	67,100		$	60,762

(1) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rates, current estimates for removal cost, the estimated remaining life of assets, and discount rates. The increase in 2017 is primarily attributed to an increase in the inflation rate and a decrease in the estimated useful life of the assets. The decrease in 2016 is primarily attributed to decreases in current estimates for removal costs and inflation rate and an increase in the estimated life of the assets.

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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

Our regulatory assets and liabilities result from our application of the provisions of Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Exchange gas offset and Prepayments and other. Current regulatory liabilities are included in Exchange gas offset. These balances are presented on our Balance Sheet on a gross basis and are recoverable or refundable over various periods. Below are the details of our regulatory assets and liabilities as of December 31, 2017 and 2016:

	2017		2016
	(Thousands of Dollars)
Current regulatory assets:
Levelized depreciation	$	4,707	$	3,864
Total current regulatory assets	4,707		3,864
Noncurrent regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	6,598		13,051
Levelized depreciation	16,149		21,849
Total noncurrent regulatory assets	22,747		34,900
Total regulatory assets	$	27,454	$	38,764
Current regulatory liabilities:
Fuel recovery	$	1,539	$	1,466
Noncurrent regulatory liabilities:
Postretirement benefits	34,089		30,587
Deferred taxes-liability	206,547		—
Asset retirement obligations, net	5,868		130
Total noncurrent regulatory liabilities	246,504		30,717
Total regulatory liabilities	$	248,043	$	32,183

The significant regulatory assets and liabilities include:

Levelized Depreciation Levelized depreciation allows contract revenue streams to remain constant over the primary contract terms by recognizing lower than book depreciation in the early years and higher than book depreciation in later years. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The difference between levelized depreciation and straight-line book depreciation is recorded as a FERC approved regulatory asset or liability and is eliminated over the levelization period.

Grossed-Up Deferred Taxes on Equity Funds Used During Construction The regulatory asset balance was 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, net This regulatory liability balance reflects the amount that we have recovered in our rates related to our future retirement costs offset by depreciation of the ARO asset and changes in the ARO liability due to the passage of time. ARO’s are expected to be fully recovered through the net negative salvage component of depreciation included in our rates. (See Note 8 for further discussion)

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.(See Note 1). In addition to this amount, as part of our 2017 rate case settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates changed due to subsequent legislation, such as the recently enacted Tax Reform, we would record a regulatory liability. As a result of Tax Reform, the regulatory liability will be $23.6 million annually for the period beginning January 1, 2018 and continuing through the time that our current rates remain effective.

Fuel Recovery These amounts reflect the value of the cumulative volumetric 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 or refunded by changing the fuel reimbursement factor in subsequent fuel filings.

Postretirement Benefits We seek to recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. These amounts are not included in the rate base, and we are not currently recovering postretirement benefit costs in our rates. (See Note 5)

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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, 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 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 customers through future rates of the future decrease in income taxes payable associated with Tax Reform. This liability was recorded in December 2017 through a regulatory charge to operating income of $206.5 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.

Our regulatory assets associated with the effects of deferred taxes on equity funds used during construction were also impacted by Tax Reform and were reduced by $5.7 million in December 2017 through a charge to Miscellaneous other (income) expenses, net below Operating income. (See Note 9 for further discussion.)

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the 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) litigation-related contingencies; 2) environmental remediation obligations; 3) impairment assessments of long-lived assets; 4) depreciation; and 5) asset retirement obligations 6) regulatory deferred tax.

Revenue Recognition

Revenue Recognition

Our revenues are primarily from services pursuant to long term firm transportation and storage agreements. These agreements provide for a reservation charge based on the volume of contracted capacity and a volumetric charge based on the volume of gas delivered, both at rates specified in our FERC tariffs. We recognize revenues for reservation charges ratably over the contract period regardless of the volume of natural gas that is transported or stored. Revenues for volumetric charges, from both firm and interruptible transportation services and storage injection and withdrawal services, are recognized based on volumes of natural gas scheduled for delivery at the agreed upon delivery point or based on volumes of natural gas scheduled for injection or withdrawal from the storage facility.

In the course of providing transportation services to our customers, we may receive or deliver different quantities of gas from shippers than the quantities delivered or received on behalf of those shippers. These transactions result in imbalances, which are typically settled through the receipt or delivery of gas in the future. Customer imbalances to be repaid or recovered in-kind are recorded as exchange gas due from others or due to others in the accompanying balance sheets. The difference between exchange gas due to us from customers and the exchange gas that we owe to customers is included in the exchange gas offset. These imbalances are valued at the average of the spot market rates at the Canadian border and the Rocky Mountain market as published in the SNL Financial “Bidweek Index - Spot Rates.” 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.

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 third-party regulatory proceedings, advice of counsel and other risks. At December 31, 2017, we had no such rate refund liabilities.

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 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 (plant), consisting principally of natural gas transmission facilities, is recorded at original cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of plant are charged or credited 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 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
Storage Facilities	1.60	%	—	2.76%
Transmission Facilities	2.80	%	—	6.97%

The incrementally priced Evergreen Expansion Project, which was an expansion of our pipeline system, was placed in service on October 1, 2003. The levelized rate design of this project creates a consistent revenue stream over the related 25-year and 15-year customer contract terms. The related levelized depreciation is lower than book depreciation in the early years and higher than book depreciation in the later years of the contract terms. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The FERC has approved the accounting for the differences between book depreciation and the Evergreen Expansion Project’s levelized depreciation as a regulatory asset.

We recorded regulatory debits totaling $4.9 million in 2017, $3.5 million in 2016, and $2.6 million in 2015 in the accompanying Statement of Comprehensive Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Project discussed above.

We record a liability and increase the basis in the underlying asset for the present value of each expected future asset retirement obligation (ARO) at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of AROs includes, 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 market-risk premium. We measure changes in the liability due to passage of time by applying an interest rate to the liability balance. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2017 and 2016 were $82.2 million and $78.5 million, respectively. The regulatory asset is expected to be fully recovered through the net negative salvage component of depreciation included in our rates; as such, the negative salvage component of accumulated depreciation ($82.2 million and $78.5 million at December 31, 2017 and 2016, respectively) has been reclassified and netted against the amount of the ARO regulatory asset.

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

We evaluate 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 such a determination has been made, our management’s estimate of undiscounted future cash flows attributable to the assets is compared to the carrying value of the assets to determine whether an impairment has occurred. If an impairment of the carrying value has occurred, the amount of the impairment recognized in the financial statements is determined by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

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. The use of alternate judgments and/or assumptions could result in the recognition of different levels of impairment charges in the financial statements.

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 is 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 $0.3 million for 2017, $0.4 million for 2016, and $0.5 million for 2015. The allowance for equity funds was $1.1 million, $1.0 million, and $1.1 million for 2017, 2016, and 2015, respectively. Both are reflected in Other (Income) and Other Expenses.

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.

Materials and Supplies Inventory

Materials and Supplies Inventory

All inventories are stated at lower of cost or net realizable value. We determine the cost of the inventories using the average cost method.

We perform an annual review of materials and supplies inventories, including an 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.

Deferred Charges

Deferred Charges

We amortize deferred charges over varying periods consistent with the FERC approved accounting treatment and recovery for such deferred items. Unamortized debt expense, debt discount and losses on reacquired long-term debt are amortized by the bonds outstanding method over the related debt repayment periods.

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 5 for further discussion.) 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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Financial Instruments (Policies)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair value of financial instruments

Fair Value of Financial Instruments

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:

Cash and advances to affiliate—The carrying amounts approximate fair value, because of the short-term nature of these instruments.

Long-term debt – The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined 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 carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.6 million and $608.8 million, respectively, at December 31, 2017, and $519.2 million and $546.8 million, respectively, at December 31, 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 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
Storage Facilities	1.60	%	—	2.76%
Transmission Facilities	2.80	%	—	6.97%

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Debt, Financing Arrangements, and Leases (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-term debt instruments

Long-term debt, presented net of unamortized discount and unamortized debt issuance costs, consists of the following:

	December 31,
	2017			2016
	(Thousands of Dollars)
5.95% senior unsecured notes due 2017	$	—		$	185,000
6.05% senior unsecured notes due 2018	250,000			250,000
7.125% unsecured debentures due 2025	85,000			85,000
4.0% unsecured debentures due 2027	250,000			—
Debt issuance costs	(2,415		)	(624		)
Unamortized debt discount	(963		)	(216		)
Total long-term debt, including current portion	$	581,622		$	519,160
Long-term debt due within one year	249,874			184,924
Total long-term debt less current portion	$	331,748		$	334,236

Maturities of long-term debt

As of December 31, 2017, cumulative maturities of outstanding long-term debt (at face value) for the next five years are as follows:

	(Thousands of Dollars)
2018: 6.05% senior unsecured notes	$	250,000
Total	$	250,000

Future minimum annual rental payments

Following are the estimated future minimum annual rental payments required under operating leases, which have initial or remaining noncancelable lease terms in excess of one year:

	(Thousands of Dollars)
2018	$	2,761
2019	2,787
Total	$	5,548

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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

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Years Ended December 31,
	2017		2016		2015
	(Thousands of Dollars)
Puget Sound Energy, Inc.	$	120,226	$	120,351	$	118,384
Northwest Natural Gas Company	51,743		49,895		50,857
Cascade Natural Gas Corporation	48,071		47,951		48,363

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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	$	60,762		$	82,454
Accretion	3,968			7,470
New obligations	149			150
Changes in estimates of existing obligations (1)	2,510			(29,312		)
Property dispositions/obligations settled	(289		)	—
Ending balance	$	67,100		$	60,762

(1) Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rates, current estimates for removal cost, the estimated remaining life of assets, and discount rates. The increase in 2017 is primarily attributed to an increase in the inflation rate and a decrease in the estimated useful life of the assets. The decrease in 2016 is primarily attributed to decreases in current estimates for removal costs and inflation rate and an increase in the estimated life of the assets.

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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 and Liabilities [Table Text Block]

Our regulatory assets and liabilities result from our application of the provisions of Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Exchange gas offset and Prepayments and other. Current regulatory liabilities are included in Exchange gas offset. These balances are presented on our Balance Sheet on a gross basis and are recoverable or refundable over various periods. Below are the details of our regulatory assets and liabilities as of December 31, 2017 and 2016:

	2017		2016
	(Thousands of Dollars)
Current regulatory assets:
Levelized depreciation	$	4,707	$	3,864
Total current regulatory assets	4,707		3,864
Noncurrent regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	6,598		13,051
Levelized depreciation	16,149		21,849
Total noncurrent regulatory assets	22,747		34,900
Total regulatory assets	$	27,454	$	38,764
Current regulatory liabilities:
Fuel recovery	$	1,539	$	1,466
Noncurrent regulatory liabilities:
Postretirement benefits	34,089		30,587
Deferred taxes-liability	206,547		—
Asset retirement obligations, net	5,868		130
Total noncurrent regulatory liabilities	246,504		30,717
Total regulatory liabilities	$	248,043	$	32,183

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Summary of Significant Accounting Policies (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Entity number of employees		0				0
Regulatory charge resulting from Tax Reform (Note 1)		$ 206,547,000	$ 0	$ 0
Revenue Recognition [Abstract]
Reserve for rate refund, Current					$ 0
Reserve for rate refund, Noncurrent					0
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory debits		4,857,000	3,510,000	2,550,000
Regulatory assets			34,900,000		22,747,000
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, debt		300,000	400,000	500,000
Allowance for funds used during construction, equity		1,104,000	953,000	1,099,000
Interest Payments [Abstract]
Cash payments for interest, net of interest capitalized		31,900,000	38,500,000	45,300,000
Levelized depreciation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory debits		4,900,000	3,500,000	$ 2,600,000
Regulatory assets			21,849,000		16,149,000
Asset retirement obligation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory assets			78,500,000		82,200,000
Negative salvage [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory assets			$ (78,500,000)		$ (82,200,000)
Operating Expense [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		206,547,000
Other Nonoperating Income (Expense) [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charge resulting from Tax Reform (Note 1)		$ 5,700,000
Minimum [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Effective Income Tax Rate Reconciliation, Deduction, Percent		21.00%
Maximum [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Effective Income Tax Rate Reconciliation, Deduction, Percent		35.00%
Financial Repositioning [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Parent, general partner ownership percentage	2.00%
Parent, limited partner ownership percentage	74.00%
Storage Facilities [Member] | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates		1.60%	1.60%	1.60%
Storage Facilities [Member] | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates		2.76%	2.76%	2.76%
Transmission Facilities [Member] | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates		2.80%	2.80%	2.80%
Transmission Facilities [Member] | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates		6.97%	6.97%	6.97%

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Rate and Regulatory Matters (Details) $ in Thousands				12 Months Ended
	Oct. 01, 2018 $ / dekatherm	Jan. 01, 2018 USD ($) $ / dekatherm	Jan. 23, 2017 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Duration of effective period of rates					5 years
Annual Cost of Service | $			$ 440,000
Regulatory Liabilities | $					$ 248,043	$ 32,183
Deferred Income Tax Charge [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities | $		$ 23,600
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Amortization Period				5 years
Subsequent Event [Member] | Phase 1 Demand Rate per Dth Pending
Public Utilities, General Disclosures [Line Items]
Demand Rate | $ / dekatherm		0.39294
Subsequent Event [Member] | Phase 1 Commodity Rate Pending
Public Utilities, General Disclosures [Line Items]
Commodity Rate | $ / dekatherm		0.00832
Subsequent Event [Member] | Phase 2 Demand Rate per Dth Pending
Public Utilities, General Disclosures [Line Items]
Demand Rate | $ / dekatherm	0.39033
Subsequent Event [Member] | Phase 2 Commodity Rate Pending
Public Utilities, General Disclosures [Line Items]
Commodity Rate | $ / dekatherm	0.00832
Subsequent Event [Member] | Deferred Income Tax Charge [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities | $		$ 23,600

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Contingent Liabilities and Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Environmental Matters
Environmental assessment and remediation costs, undiscounted	$ 3.0
Accrued environmental liabilities	3.0	$ 4.4
Accrued Environmental Loss Contingencies, Current	1.3	1.3
Accrued Environmental Loss Contingencies, Noncurrent	$ 1.7	$ 3.1

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Debt, Financing Arrangements, and Leases (Details) - USD ($)				12 Months Ended
	Apr. 15, 2017	Feb. 02, 2015	Oct. 02, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt issuance costs				$ (2,415,000)	$ (624,000)
Unamortized debt discount				(963,000)	(216,000)
Long-term debt due within one year				249,874,000	184,924,000
Total long-term debt, including current portion				331,748,000	334,236,000
Total long-term debt				331,748,000	334,236,000
Maturities of long-term debt
2018: 6.05% senior unsecured notes				250,000,000
2019				0
2020				0
2021				0
2022				0
Total				250,000,000
Extinguishment of Debt [Line Items]
Retirement of Long-Term Debt	$ 185,000,000
Line of Credit Facility [Line Items]
Lease, initial term			10 years
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018				2,761,000
2019				2,787,000
Total				5,548,000
Operating Leases, Rent Expense, Net [Abstract]
Operating lease rent expense, net of sublease revenues				3,500,000	2,700,000	$ 2,700,000
Minimum [Member]
Line of Credit Facility [Line Items]
Lease, renewal term			5 years
Maximum [Member]
Line of Credit Facility [Line Items]
Lease, renewal term			10 years
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
Williams Partners L.P. [Member] | Rate addition to federal funds effective rate [Member]
Line of Credit Facility [Line Items]
Line of credit facility, basis spread on variable rate		0.50%
Williams Partners L.P. [Member] | Rate addition to London interbank offered rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of credit facility, basis spread on variable rate		1.00%
5.95% senior unsecured notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt				$ 0	185,000,000
Interest rate stated percentage				5.95%
6.05% senior unsecured notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt				$ 250,000,000	250,000,000
7.125% unsecured debentures due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt				85,000,000	85,000,000
4% Senior Unsecured Notes Due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt				$ 250,000,000	$ 0
Interest rate stated percentage				4.00%
Proceeds from Issuance of Unsecured Debt	$ 250,000,000
$3.5 billion credit facility | 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
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
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

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Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Salaries, Wages and Officers' Compensation [Abstract]
Stock-based compensation expense	$ 1,900	$ 1,400	$ 1,500
Defined Benefit Plan Disclosure [Line Items]
Pension cost	5,200	2,300	4,400
Regulatory liabilities	246,504	30,717
Defined contribution plan matching contributions expense	2,100	2,200	2,200
Retiree health care and life insurance benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	3,500	3,800	$ 3,400
Other Postretirement Benefit Costs
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	34,100	$ 30,600
Pension Plan [Member] | Directly charged [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	3,000
Pension Plan [Member] | Allocated corporate expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 1,100

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Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Estimate of fair value [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, including current maturities	$ 608,800	$ 546,800
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, including current maturities	$ 581,622	$ 519,160

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Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017
Related Party Transaction [Line Items]
Advances to affiliate			$ 45,137		$ 137,666
Related party transaction, rate		1.16%
Entity number of employees		0				0
Related party transaction, expenses from transactions with related party		$ 96,500	92,800	$ 100,400
Severance Costs			2,400
Cash distributions to parent		186,000	174,000	168,000
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 34,000
Puget Sound Energy, Inc. [Member]
Revenue, Major Customer [Line Items]
Operating revenues		120,226	120,351	118,384
Northwest Natural Gas Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues		51,743	49,895	50,857
Cascade Natural Gas Corporation [Member]
Revenue, Major Customer [Line Items]
Operating revenues		$ 48,071	$ 47,951	$ 48,363

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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	$ 60,762	$ 82,454
Accretion	3,968	7,470
New obligations	149	150
Changes in estimates of existing obligations (1)	2,510	(29,312)
Property dispositions/obligations settled	(289)	0
Ending balance	$ 67,100	$ 60,762

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Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Current regulatory assets		$ 4,707	$ 3,864
Noncurrent regulatory assets		22,747	34,900
Total regulatory assets		27,454	38,764
Regulatory Liabilities [Line Items]
Regulatory liabilities		246,504	30,717
Total regulatory liabilities		248,043	32,183
Fuel recovery [Member]
Regulatory Liabilities [Line Items]
Current regulatory liabilities		1,539	1,466
Postretirement benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities		34,089	30,587
Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities		206,547	0
Total regulatory liabilities	$ 23,600
Asset retirement obligations, net [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities		5,868	130
Levelized depreciation [Member]
Regulatory Assets [Line Items]
Current regulatory assets		4,707	3,864
Noncurrent regulatory assets		16,149	21,849
Deferred taxes on equity funds used during construction [Member]
Regulatory Assets [Line Items]
Noncurrent regulatory assets		$ 6,598	$ 13,051