10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

☑	ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
	For the fiscal year ended	December 31, 2020
	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)

801 583-8800

(Registrant’s telephone number, including area code)

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

None

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

None

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

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

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

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted 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 such files).  Yes  þ    No  ¨

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 ☐

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 has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ¨

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	18
Item 2. PROPERTIES	18
Item 3. LEGAL PROCEEDINGS	18
Item 4. MINE SAFETY DISCLOSURES	18
PART II
Item 5. MARKET FOR REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES	19
Item 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS	19
Item 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK	21
Item 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA	22
Item 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE	45
Item 9A. CONTROLS AND PROCEDURES	45
Item 9B. OTHER INFORMATION	46
PART III
Item 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE (Omitted)	46
Item 11. EXECUTIVE COMPENSATION (Omitted)	46
Item 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS (Omitted)	46
Item 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE (Omitted)	46
Item 14. PRINCIPAL ACCOUNTING FEES AND SERVICES	46
PART IV
Item 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES	47
Item 16. FORM 10-K SUMMARY	48

1

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

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

Northwest is indirectly owned by The Williams Companies, Inc. (Williams), a publicly traded Delaware corporation.

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 42 transmission compressor stations. Our compression facilities have a combined sea level-rated capacity of approximately 473,000 horsepower. At December 31, 2020, 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 undivided 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 public utilities, municipalities, 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 2020, our three largest customers were Puget Sound Energy, Inc., Northwest Natural Gas Company, and Cascade Natural Gas Corporation, which accounted for approximately 29.5 percent, 10.9 percent, and 10.6 percent, respectively, of our total operating revenues for the year ended December 31, 2020. 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 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.

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FERC Developments

Notice of Inquiry (Docket No. PL19-4-000). On May 21, 2020, the FERC issued a “Policy Statement on Determining Return on Equity for Natural Gas and Oil Pipelines” (Policy Statement) in Docket No. PL19-4-000 adopting changes to its policies concerning the calculation of a public utility return on equity (ROE). In this Policy Statement, the FERC revised its ROE policy for natural gas pipelines and oil pipelines to provide that the FERC will determine a pipeline’s ROE by averaging the results of the Discounted Cash Flow model and the Capital Asset Pricing Model, with each weighted equally. The FERC declined to adopt any additional policy changes at this time and will address all other issues concerning the determination of a pipeline’s ROE as they arise in future proceedings.

Our next general rate case must be filed for new rates to become effective no later than January 1, 2023.

                        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 approximately $1.3 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 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.

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 5. Contingent Liabilities and Commitments – Environmental Matters.”

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Safety and Maintenance

Our operations are subject to the Natural Gas Pipeline Safety Act of 1968, as amended, the Pipeline Safety Improvement Act of 2002, the Pipeline Safety, Regulatory Certainty, and Jobs Creation Act of 2011 (Pipeline Safety Act), and the Protecting Our Infrastructure of Pipelines and Enhancing Safety Act of 2016, which regulate safety requirements in the design, construction, operation, and maintenance of interstate natural gas transmission facilities. The United States Department of Transportation 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.

In 2016, PHMSA published a proposed rulemaking that would impose new or more stringent requirements for certain natural gas pipelines including, expanding certain of PHMSA’s current regulatory safety programs for natural gas lines in high-population areas (also known as moderate consequence areas (MCAs)) that do not qualify as high consequence areas (HCAs) and requiring maximum allowable operating pressure (MAOP) validation through re-verification of all historical records for pipelines in service, which may require natural gas pipelines installed before 1970 (previously excluded from certain pressure testing obligations) to be pressure tested. However, PHMSA has since decided to split this proposed rule (Mega Rule), into three separate rulemaking proceedings. The first of these three rulemakings, relating to onshore gas transmission pipelines, was published as a final rule on October 1, 2019, and imposes numerous requirements, including MAOP reconfirmation, the periodic assessment of additional pipeline mileage outside of HCAs, the reporting of exceedances of MAOP, and the consideration of seismicity as a risk factor in integrity management. In accordance with the final rule, we have developed new procedures and updated our existing Pipeline Safety Program to facilitate meeting all requirements within the time frames stated. The remaining rulemakings comprising the Mega Rule are expected to be issued in 2021 and will include revised pipeline repair criteria as well as more stringent corrosion control requirements.

We are also expecting additional regulations due to new pipeline safety legislation finalized in December 2020 that reauthorized PHMSA pipeline safety programs. The new legislation includes mandates for PHMSA to publish final rules for advanced leak detection for gas pipelines, additional repair criteria for gas pipelines, and updated operations and maintenance standards requirements applicable to large-scale liquefied natural gas facilities.

New regulations adopted by PHMSA may impose more stringent requirements applicable to integrity management programs and other pipeline safety aspects of our operations, which could cause us to incur increased capital and operating costs and operational delays.

Pipeline Integrity Regulations We have an enterprise-wide Gas Integrity Management Plan that we believe meets 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. We estimate that the cost to be incurred in 2021 associated with this program will be approximately $31 million. 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 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 9. Transactions with Major Customers and Affiliates.”

5

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 such as “anticipates,” “believes,” “seeks,” “could,” “may,” “should,” “continues,” “estimates,” “expects,” “forecasts,” “intends,” “might,” “goals,” “objectives,” “targets,” “planned,” “potential,” “projects,” “scheduled,” “will,” “assumes,” “guidance,” “outlook,” “in-service date,” or other similar expressions. These forward-looking statements are based on management’s beliefs and assumptions and on information currently available to management and include, among others, statements regarding:

•Our and our affiliates’ future credit ratings;

•Amounts and nature of future capital expenditures;

•Expansion and growth of our business and operations;

•Expected in-service dates for capital projects;

•Financial condition and liquidity;

•Business strategy;

•Cash flow from operations or results of operations;

•Rate case filings;

•Natural gas prices, supply, and demand;

•Demand for our services; and

•The impact of the coronavirus (COVID-19) pandemic.

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 the forward-looking statements include, among others, the following:

•The impact of operational and developmental hazards and unforeseen interruptions;

•Development and rate of adoption of alternative energy sources;

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

•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;

•Changes in maintenance and construction costs, as well as our ability to obtain sufficient construction-related inputs, including skilled labor;

6

•The impact of existing and future laws and 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;

•Increasing scrutiny and changing expectations from stakeholders with respect to our environmental, social, and governance practices;

•The physical and financial risks associated with climate change;

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

•Our ability to successfully expand our facilities and operations;

•Whether we are able to successfully identify, evaluate, and timely execute our capital projects and investment opportunities;

•Risks related to financing, including restrictions stemming from debt agreements, future changes in credit ratings as determined by nationally recognized credit rating agencies, and the availability and cost of capital;

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

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

•The risks resulting from outbreaks or other public health crises, including COVID-19;

•Changes in the current geopolitical situation;

•Changes in U.S. governmental administration and policies;

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

•Acts of terrorism, cybersecurity incidents, 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 announce publicly the result of 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.

7

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;

•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 other 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 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

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•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.

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, Williams and its other affiliates 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.

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

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

Public and regulatory scrutiny of the energy industry has resulted in the proposal and/or implementation of increased regulations. Such scrutiny has also resulted in various inquiries, investigations, and court proceedings, including litigation of energy industry matters. Both the customers on our system 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 that differs from prior regulatory action. New laws and regulations might also be adopted or become applicable to us, our customers, or our business activities. The change in the U.S. governmental administration and its policies may increase the likelihood of such legal and regulatory developments. 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.

Increasing scrutiny and changing expectations from stakeholders with respect to our environmental, social and governance practices may impose additional costs on us or expose us to new or additional risks.

Companies across all industries are facing increasing scrutiny from stakeholders related to their environmental, social, and governance (“ESG”) practices. Investor advocacy groups, certain institutional investors, investment funds, and other influential investors are also increasingly focused on ESG practices and in recent years have placed increasing importance on the implications and social cost of their investments. Regardless of the industry, investors’ increased focus and activism related to ESG and similar matters may hinder access to capital, as investors may decide to reallocate capital or to not commit capital as a result of their assessment of a company’s ESG practices. Companies that do not adapt to or comply with investor or other stakeholder expectations and standards, which are evolving, or that are perceived to have not responded appropriately to the growing concern for ESG issues, regardless of whether there is a legal requirement to do so, may suffer from reputational damage and the business, financial condition, and/or stock price of such a company could be materially and adversely affected.

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We face pressures from our stakeholders, who are increasingly focused on climate change, to prioritize sustainable energy practices, reduce our carbon footprint and promote sustainability. Our stakeholders may require us to implement ESG procedures or standards in order to continue engaging with us, to remain invested in us, or before they will make further investments in us. Additionally, we may face reputational challenges in the event our ESG procedures or standards do not meet the standards set by certain constituencies. We have adopted certain practices as highlighted in Williams’ 2018 Sustainability Report, including with respect to air emissions, biodiversity and land use, climate change, and environmental stewardship. It is possible, however, that our stakeholders might not be satisfied with our sustainability efforts or the speed of their adoption. If we do not meet our stakeholders’ expectations, our business and/or our ability to access capital could be harmed.

Additionally, adverse effects upon the oil and gas industry related to the worldwide social and political environment, including uncertainty or instability resulting from climate change, changes in political leadership and environmental policies, changes in geopolitical-social views toward fossil fuels and renewable energy, concern about the environmental impact of climate change, and investors’ expectations regarding ESG matters, may also adversely affect demand for our services. Any long-term material adverse effect on the oil and gas industry could have a significant financial and operational adverse impact on our business.

The occurrence of any of the foregoing could have a material adverse effect on our business and financial condition.

We may be subject to physical and financial risks associated with climate change.

The threat of global climate change may create physical and financial risks to our business. Energy needs vary with weather conditions. To the extent weather conditions may be affected by climate change, energy use could increase or decrease depending on the duration and magnitude of any changes. Increased energy use due to weather changes may require us to invest in more pipelines and other infrastructure to serve increased demand. A decrease in energy use due to weather changes may affect our financial condition through decreased revenues. Extreme weather conditions in general require more system backup, adding to costs, and can contribute to increased system stresses, including service interruptions. Weather conditions outside of our operating territory could also have an impact on our revenues. To the extent the frequency of extreme weather events increases, this could increase our cost of providing service. We may not be able to pass on the higher costs to our customers or recover all costs related to mitigating these physical risks.

Additionally, many climate models indicate that global warming is likely to result in rising sea levels and increased frequency and severity of weather events, which may lead to higher insurance costs, or a decrease in available coverage, for our assets in areas subject to severe weather. These climate-related changes could damage our physical assets, especially operations located in low-lying areas near river banks, and facilities situated in rain-susceptible regions.

To the extent financial markets view climate change and greenhouse gas (“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. Our business could also be affected by the potential for lawsuits against GHG emitters, based on links drawn between GHG emissions and climate change.

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 these 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

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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 regulations and the costs that may be associated with such regulation and with the regulation of emissions of GHGs have the potential to affect our business. Regulatory actions by the U.S. Environmental Protection Agency or the passage of new climate change laws or regulations could result in increased costs to operate and maintain our facilities, install new emissions controls on our facilities, or administer and manage any GHG emissions program. We believe it is possible that future governmental legislation and/or regulation may require us either to limit GHG emissions associated with our operations or to purchase allowances for such emissions. However, we cannot predict precisely what form these future regulations might take, the stringency of any such regulations or when they might become effective. Several legislative bills have been introduced in the United States Congress that would require carbon dioxide emission reductions. Previously considered proposals have included, among other things, limitations on the amount of GHGs that can be emitted (so called “caps”) together with systems of permitted emissions allowances. These proposals could require us to reduce emissions or to purchase allowances for such emissions.

In addition to activities on the federal level, state and regional initiatives could also lead to the regulation of GHG emissions sooner than and/or independent of federal regulation. These regulations could be more stringent than any federal legislation that may be adopted. Future legislation and/or regulation designed to reduce GHG emissions could make some of our activities uneconomic to maintain or operate. We continue to monitor legislative and regulatory developments in this area and otherwise take efforts to limit and reduce GHG emissions from our facilities. Although the regulation of GHG emissions may have a material impact on our operations and rates, we believe it is premature to attempt to quantify the potential costs of the impacts.

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.

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, 2020, our largest customer was Puget Sound Energy, Inc., which accounted for approximately 29.5 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, are required to make pre-payments or provide security to satisfy credit concerns, or are dependent upon us, in some cases without a readily available alternative, to provide necessary services. 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 have been or could be negatively impacted, causing them significant economic stress resulting, in some cases, in a customer bankruptcy filing or an effort to renegotiate our contracts. To the extent one or more of our key customers commences bankruptcy proceedings, our contracts with such customers may be subject to rejection under applicable provisions of the United States Bankruptcy Code, or, if we so agree, 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

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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 facilities on land owned by third parties and governmental agencies for a specific period of time. Our loss of any of these rights, through our inability to renew right-of-way contracts or otherwise, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We face opposition to operation and expansion of our pipelines and facilities from various individuals and groups.

We have experienced, and we anticipate that we will continue to face, opposition to the operation and expansion of our pipelines and facilities from governmental officials, environmental groups, landowners, tribal groups, local groups, and other advocates. In some instances, we encounter opposition that disfavors hydrocarbon-based energy supplies regardless of practical implementation or financial considerations. Opposition to our operation and expansion can take many forms, including the delay or denial of required governmental permits, organized protests, attempts to block or sabotage our operations, intervention in regulatory or administrative proceedings involving our assets, or lawsuits or other actions designed to prevent, disrupt, or delay the operation or expansion of our assets and business. In addition, acts of sabotage or eco-terrorism could cause significant damage or injury to people, property, or the environment or lead to extended interruptions of our operations. Any such event that delays or prevents the expansion of our business, that interrupts the revenues generated by our operations, or which causes us to make significant expenditures not covered by insurance, could adversely affect our financial condition and results of operations.

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. 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 that are materially different than anticipated;

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•We could be required to contribute additional capital to support acquired businesses or assets and 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.

Chemical substances in the natural gas our pipeline systems transport could cause damage or affect the ability of our pipeline systems or third-party equipment to function properly, which may result in increased preventative and corrective action costs and may impact our relationships with our customers.

We have identified the presence of a chemical substance, dithiazine, in facilities located on our system.The facilities in which dithiazine has been detected on our system are located downstream of the interconnecting and unaffiliated pipeline of Gas Transmission Northwest (GTN), which has reported the presence of dithiazine in its system. Therefore, we believe that the dithiazine found in our system is attributable to gas received from GTN.

Dithiazine may result in improper functioning of equipment if not cleaned properly. We may incur costs and experience operational delays in connection with cleaning dithiazine from our systems. Some of our customers downstream of our facilities have also detected dithiazine in their facilities and any impacts on affected customers may impact our relationships with those customers.

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’ credit ratings.

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

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, 2020 was $578.0 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 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’ debt agreements contain similar covenants with respect to Williams and its subsidiaries, including us.

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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 (including as a result of the COVID-19 pandemic) 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, along with Williams and Transcontinental Gas Pipe Line Company, LLC, are party to a credit agreement with aggregate commitments available of $4.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. We and Transcontinental Gas Pipe Line Company, LLC are each subject to a $500 million borrowing sublimit. As of December 31, 2020, we had a borrowing capacity of $500 million under such 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.

Williams 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 Williams, Williams 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;

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•Mergers or other business combinations; and

•Acquisition or disposition of assets.

Williams 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 and storage assets, 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 pipeline and storage facilities;

•Accounts and records;

•Depreciation and amortization policies;

•Relationships with affiliated companies that 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.

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 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 arrangements could be disrupted. Similarly, the expiration of agreements associated with such arrangements 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.

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 for defined benefit pension plans and other postretirement benefit plans. 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

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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

We face risks related to the COVID-19 pandemic and other health epidemics.

The global outbreak of COVID-19 is currently impacting countries, communities, supply chains, and markets. We provide a critical service to our customers, which means that it is paramount that we keep our employees safe. To date, COVID-19 has not had a material impact on our business. However, we cannot predict whether, and the extent to which, COVID-19 will have a material impact on our business, including our liquidity, financial condition, and results of operations. COVID-19 could pose a risk to our employees, our customers, our suppliers, and the communities in which we operate, which could negatively impact our business. To the extent that our access to the capital markets is adversely affected by COVID-19, we may need to consider alternative sources of funding for our operations and for working capital, any of which could increase our cost of capital. Measures to try to contain the virus, such as travel bans and restrictions, quarantines, shelter in place orders, and shutdowns, may cause us to experience operational delays or to delay plans for growth. The extent to which COVID-19 may impact our business will depend on future developments, which are highly uncertain and cannot be predicted, including new information concerning the severity of COVID-19 and the actions taken to contain it or treat its impact, among others.

To the extent the COVID-19 pandemic adversely affects our business and financial results, it may also have the effect of heightening many of the other factors described in this report.

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.

Our business could be negatively impacted by acts of terrorism 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.

A breach of our information technology infrastructure, including a breach caused by a cybersecurity attack on us or third parties with whom we are interconnected, may interfere with the safe operation of our assets, result in the disclosure of personal or proprietary information, and harm our reputation.

We rely on our information technology infrastructure to process, transmit, and store electronic information, including information we use to safely operate our assets. In addition to the oversight of our business provided by our Management Committee, the Williams’ Board of Directors has oversight responsibility with regard to enterprise-wide assessment of the major risks inherent in its businesses, including cybersecurity risks. Accordingly, the Williams’ Board of Directors reviews management’s efforts to address and mitigate such risks, including the establishment and implementation of policies to address cybersecurity threats. We have invested, and expect to continue to invest, significant time, manpower, and capital in our information technology infrastructure. However, 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. While we believe that we maintain appropriate information security policies, practices, and protocols, we regularly 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 face unlawful attempts to gain access to our information technology infrastructure, including coordinated attacks from hackers, whether state-sponsored groups, “hacktivists”, or private individuals. We face the threat of theft and misuse of sensitive data and information, including customer and employee information. We also face attempts to gain access to information related to our assets

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through attempts to obtain unauthorized access by targeting acts of deception against individuals with legitimate access to physical locations or information. We also are subject to cybersecurity risks arising from the fact that our business operations are interconnected with third parties, including third-party pipelines, other facilities, and our contractors and vendors. In addition, the breach of certain business systems could affect our ability to correctly record, process, and report financial 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 or destruction of our assets, unnecessary waste, safety incidents, damage to the environment, reputational damage, potential liability, the loss of contracts, the imposition of significant costs associated with remediation and litigation, heightened regulatory scrutiny, increased insurance costs, and have a material adverse effect on our operations, financial condition, results of operations, and cash flows.

General Risk Factors

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.

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.

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

While it is not possible for us to predict the final outcome of any pending legal proceedings involving governmental authorities under federal, state, and local laws regulating the discharge of materials into the environment, we do not anticipate a material effect on our financial position if we were to receive an unfavorable outcome in any one or more of such proceedings. Our threshold for disclosing material environmental legal proceedings involving a governmental authority where potential monetary sanctions are involved is $1 million.

The information called for by this item is provided in “Item 8. Financial Statements and Supplementary Data – Notes to Financial Statements: Note 5. 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, 2020, we were indirectly owned by Williams.

We paid $164.0 million and $110.0 million in cash distributions to our parent during 2020 and 2019, respectively. During February 2021, we declared and paid cash distributions of $55.0 million to our parent.

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

The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions. We believe that the nature of these estimates and assumptions is material due to the subjectivity and judgment necessary, or the susceptibility of such matters to change, and the impact of these on our financial condition or results of operations.

Regulatory Accounting

We are regulated by the FERC. Accounting Standards Codification (ASC) Topic 980, Regulated Operations, (Topic 980) provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. 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 Net Income for the period in which the discontinuance of regulatory accounting treatment occurs, unless otherwise required to be recorded under other provisions of U.S. generally accepted accounting principles. The aggregate amount of regulatory assets reflected in the Balance Sheet is $21.4 million at December 31, 2020. The aggregate amount of regulatory liabilities reflected in the Balance Sheet is $359.0 million at December 31, 2020. A summary of regulatory assets and liabilities is included in Note 11. Regulatory Assets and Liabilities of Notes to Financial Statements.

19

RESULTS OF OPERATIONS

Analysis of Financial Results

This analysis discusses financial results of our operations for the years 2020 and 2019. 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.

Operating Revenues increased $5.1 million, or 1 percent, in 2020 as compared with 2019 primarily due to:

•$6.6 million higher natural gas transportation revenues as a result of placing the North Seattle Upgrade into service in late 2019, the absence of an adjustment correcting a contract liability recorded in 2019, partially offset by the termination of several maximum rate contracts in 2019.

•The increase in natural gas transportation revenues was partly offset by a $1.7 million decrease in natural gas storage primarily as a result of a decrease in the use of park and loan services and lower demand for interruptible storage space in 2020 compared to 2019.

Transportation service accounted for 97 percent and gas storage service accounted for 3 percent of our operating revenues in 2020 and 96 percent and 4 percent, respectively, in 2019.

Operating Expenses decreased $9.8 million, or 4 percent, in 2020 as compared with 2019, mostly due to:

•$11.6 million decrease in employee labor and benefits costs, partially offset by higher relocation expenses due to a voluntary separation program and restructuring initiated by Williams in 2019 as well as the favorable impact of a change in an employee benefit policy,

•$3.7 million lower operating and maintenance costs primarily contractor services,

•$4.1 million increase in depreciation due to increased plant additions, and

•$1.9 million increase in property taxes, primarily associated with a property tax adjustment in 2019.

Other (income) and other expenses had a unfavorable change of $6.5 million, or 30 percent, in 2020 primarily due to lower interest income as a result of a lower interest rates on the intercompany note receivable balance and lower Allowance for funds used during construction - equity and borrowed as a result of lower capital expenditures in 2020 compared to 2019.

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

CAPITAL RESOURCES AND LIQUIDITY

Method of Financing

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

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 Williams and Transcontinental Gas Pipe Line Company, LLC (Transco), are co-borrowers under a $4.5 billion unsecured credit facility. Total letter of credit capacity available to Williams under the credit facility is $1.0 billion. We may borrow up to $500 million under the credit facility to the extent not otherwise utilized by Williams and Transco.

We are a participant in Williams’s cash management program, and we make advances to and receive advances from Williams. At December 31, 2020, our advances to Williams totaled approximately $247.9 million. These advances are represented by demand notes.

Please see “Item 8. Financial Statements and Supplementary Data – Notes to Financial Statements: Note 6. Debt and Financing Arrangements – Credit Facility and Note 9. Transactions with Major Customers and Affiliates – Related Party Transactions.”

20

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 2021 capital expenditures will be approximately $81 million. In 2021, we expect to fund our capital expenditures with cash from operations.

Recent Developments

COVID-19

The outbreak of COVID-19 has severely impacted global economic activity and caused significant volatility and negative pressure in financial markets. We are monitoring the COVID-19 pandemic and have taken steps intended to protect the safety of our customers, employees and communities, and to support the continued delivery of safe and reliable service to our customers and the communities we serve. We are continuing to monitor developments with respect to the outbreak and note the following:

•Our financial condition, results of operations, and liquidity have not been materially impacted by direct effects of COVID-19.

•We believe we have the ability to access the debt market if necessary, and continue to have significant levels of unused capacity on our revolving credit facility with no significant debt maturities in the near future.

•We continue to monitor and adapt our remote working arrangements and limit business-related travel. Implementation of these measures has not required material expenditures or significantly impacted our ability to operate our business.

•Our remote working arrangements have not significantly impacted our internal controls over financial reporting and disclosure controls and procedures.

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, 2020
Fixed rates on long-term debt:
7.125% unsecured debentures due 2025	$	85,000
4.0% unsecured debentures due 2027	500,000
	585,000
Unamortized debt issuance costs	(3,581)
Unamortized debt discount	(3,401)
Total long-term debt, including current portion	$	578,018

Our total long-term debt at December 31, 2020 had a carrying value of $578.0 million and a fair market value of $680.6 million. As of December 31, 2020, the weighted-average interest rate on our long-term debt was 4.45 percent.

21

Item 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

INDEX TO FINANCIAL STATEMENTS

	Page
Report of Independent Registered Public Accounting Firm	23
Statement of Net Income	25
Balance Sheet	26
Statement of Member's Equity	28
Statement of Cash Flows	29
Notes to Financial Statements	30

22

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 sheets of Northwest Pipeline LLC (the Company) as of December 31, 2020 and 2019, the related statements of net income, member’s equity and cash flows for each of the three years in the period ended December 31, 2020, 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, 2020 and 2019, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2020, 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.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current period audit of the financial statements that was communicated or required to be communicated to the audit committee and that: (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of the critical audit matter does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by

23

communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Description of the Matter

Regulatory Assets and Liabilities As discussed in Note 1 to the financial statements, the Company is an interstate natural gas transmission company that is regulated by the Federal Energy Regulatory Commission (“FERC”) and applies accounting principles in Topic 980 for regulated operations. As such, certain incurred costs that would otherwise be charged to expense are deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense are deferred as regulatory liabilities, based on the expected return to customers in future rates. The Company records items as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refund in future rates. Auditing regulatory assets and liabilities is complex as it requires specialized knowledge of rate-regulated activities and judgments as to matters that could affect the recording of regulatory assets and liabilities.

How We Addressed the Matter in Our Audit

We obtained an understanding, evaluated the design, and tested the operating effectiveness of internal controls over the Company’s accounting for regulatory assets and liabilities, including, among others, controls over the evaluation of filings with regulatory bodies and their effects on existing regulatory assets and liabilities, including factors that may affect the timing or nature of recoverability. We performed audit procedures that included, among others, reviewing evidence of correspondence with regulatory bodies to test that the Company evaluated information obtained from regulatory rulings. For example, we assessed the recoverability, considering information obtained from the Company’s stipulation and settlement agreement, for various regulatory assets including levelized depreciation. In addition, we tested calculations of material regulatory assets and liabilities, including that amortization for certain regulatory assets and liabilities corresponded to relevant regulatory filings and/or orders. For example, we tested whether the calculation of regulatory liabilities attributable to changes in tax rates was consistent with methods agreed to by regulatory bodies.

/s/ Ernst & Young LLP

We have served as the Company’s auditor since 1986.

Houston, Texas

February 24, 2021

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NORTHWEST PIPELINE LLC

STATEMENT OF NET INCOME

(Thousands of Dollars)

	Years Ended December 31,
	2020		2019		2018
OPERATING REVENUES:
Natural gas transportation	$	435,238	$	428,656	$	430,730
Natural gas storage	14,268		15,975		12,852
Other	(24)		(209)		36
Total operating revenues	449,482		444,422		443,618
OPERATING EXPENSES:
General and administrative	47,695		51,665		50,653
Operation and maintenance	69,970		81,736		75,237
Depreciation and amortization	112,004		107,951		106,073
Regulatory debits	1,148		1,107		2,334
Taxes, other than income taxes	16,290		14,388		17,507
Regulatory charges resulting from tax rate changes	23,580		23,580		35,680
Other (income) expenses, net	(38)		47		444
Total operating expenses	270,649		280,474		287,928
OPERATING INCOME	178,833		163,948		155,690
OTHER (INCOME) AND OTHER EXPENSES:
Interest expense	29,712		29,232		27,987
Allowance for equity and borrowed funds used during construction	(669)		(3,418)		(2,183)
Miscellaneous other (income) expenses, net	(1,296)		(4,533)		(1,575)
Total other (income) and other expenses	27,747		21,281		24,229
NET INCOME	$	151,086	$	142,667	$	131,461

See accompanying notes.

25

NORTHWEST PIPELINE LLC

BALANCE SHEET

(Thousands of Dollars)

	December 31, 2020		December 31, 2019
ASSETS
CURRENT ASSETS:
Cash	$	—	$	—
Receivables:
Trade	37,365		40,066
Affiliated companies	51		109
Advances to affiliate	247,869		201,265
Other	840		1,962
Materials and supplies	9,807		9,683
Exchange gas due from others	4,466		5,534
Prepayments and other	4,078		3,346
Total current assets	304,476		261,965
PROPERTY, PLANT AND EQUIPMENT, at cost	3,653,792		3,593,186
Less-Accumulated depreciation	1,761,229		1,673,315
Total property, plant and equipment, net	1,892,563		1,919,871
OTHER ASSETS:
Deferred charges	3,775		1,075
Regulatory assets	20,022		21,935
Right-of-use assets	10,692		18,101
Total other assets	34,489		41,111
Total assets	$	2,231,528	$	2,222,947

See accompanying notes.

26

NORTHWEST PIPELINE LLC

BALANCE SHEET

(Thousands of Dollars)

	December 31, 2020		December 31, 2019
LIABILITIES AND MEMBER’S EQUITY
CURRENT LIABILITIES:
Payables:
Trade	$	16,157	$	15,635
Affiliated companies	4,110		9,172
Accrued liabilities:
Taxes, other than income taxes	10,905		9,913
Interest	5,505		5,505
Exchange gas due to others	4,557		4,468
Customer advances	539		4,109
Other	6,786		6,990
Total current liabilities	48,559		55,792
LONG-TERM DEBT	578,018		577,045
OTHER NON-CURRENT LIABILITIES:
Asset retirement obligations	95,777		91,251
Regulatory liabilities	355,725		323,032
Lease liability	8,341		16,823
Other	4,713		5,695
Total other non-current liabilities	464,556		436,801
CONTINGENT LIABILITIES AND COMMITMENTS (Note 5)
MEMBER'S EQUITY:
Member’s capital	1,073,892		1,073,892
Retained earnings	66,503		79,417
Total member’s equity	1,140,395		1,153,309
Total liabilities and member’s equity	$	2,231,528	$	2,222,947

See accompanying notes.

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NORTHWEST PIPELINE LLC

STATEMENT OF MEMBER’S EQUITY

(Thousands of Dollars)

	Years Ended December 31,
	2020		2019		2018
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	79,417		46,750		89,289
Net income	151,086		142,667		131,461
Cash distributions to parent	(164,000)		(110,000)		(174,000)
Balance at end of period	66,503		79,417		46,750
Total member’s equity	$	1,140,395	$	1,153,309	$	1,120,642

See accompanying notes.

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NORTHWEST PIPELINE LLC

STATEMENT OF CASH FLOWS

(Thousands of Dollars)

	Years Ended December 31,
	2020		2019		2018
OPERATING ACTIVITIES:
Net income	$	151,086	$	142,667	$	131,461
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	112,004		107,951		106,073
Regulatory debits	1,148		1,107		2,334
Regulatory charges resulting from tax rate changes	23,580		23,580		35,680
Amortization of deferred charges and credits	(3,526)		(2,806)		954
Allowance for equity funds used during construction (equity AFUDC)	(414)		(2,744)		(1,703)
Changes in current assets and liabilities:
Trade and other accounts receivable	3,606		(1,528)		(1,611)
Affiliated receivables	58		(91)		1,903
Materials and supplies	(124)		363		39
Other current assets	337		4,311		4,494
Trade accounts payable	5,140		(1,497)		1,753
Affiliated payables	(5,062)		(17,360)		15,234
Other accrued liabilities	(8,603)		(8,056)		881
Changes in non-current assets and liabilities:
Regulatory liabilities	4,185		3,493		2,530
Other, net	503		8,570		(4,894)
Net cash provided by operating activities	283,918		257,960		295,128
FINANCING ACTIVITIES:
Proceeds from long-term debt	—		—		246,395
Retirement of long-term debt	—		—		(250,000)
Payments for debt issuance costs	—		(59)		(2,498)
Cash distributions to parent	(164,000)		(110,000)		(174,000)
Net cash used in financing activities	(164,000)		(110,059)		(180,103)
INVESTING ACTIVITIES:
Property, plant and equipment:
Capital expenditures*	(78,497)		(128,440)		(73,487)
Contributions and advances for construction costs	6,103		4,805		2,075
Disposal of property, plant and equipment, net	(920)		(3,401)		(879)
Advances to affiliates, net	(46,604)		(20,865)		(42,734)
Net cash used in investing activities	(119,918)		(147,901)		(115,025)
NET (DECREASE) INCREASE IN CASH	—		—		—
CASH AT BEGINNING OF PERIOD	—		—		—
CASH AT END OF PERIOD	$	—	$	—	$	—
____________________________________
* Increases to property, plant and equipment, exclusive of equity AFUDC	$	(78,602)	$	(132,260)	$	(73,105)
Changes in related accounts receivable, accounts payable, and accrued liabilities	105		3,820		(382)
Capital expenditures	$	(78,497)	$	(128,440)	$	(73,487)

 See accompanying notes.

29

NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Corporate Structure and Control

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

Northwest Pipeline LLC (Northwest) was indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which was consolidated by The Williams Companies, Inc. (Williams). On August 10, 2018, Williams completed a merger with WPZ, pursuant to which Williams acquired all of the publicly held outstanding common units of WPZ in exchange for shares of Williams’ common stock (WPZ Merger). Williams continued as the surviving entity. Northwest is now indirectly owned by Williams.

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

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). Accounting Standards Codification (ASC) Regulated Operations, (Topic 980) provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. 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.

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; 5) asset retirement obligations; and 6) regulatory deferred tax.

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipelines business and are not within the scope of Accounting Standards Update (ASU) 2014-09, Revenues from Contracts with Customers (ASC 606). Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed assets.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Most of our firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas scheduled, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended beyond the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts - an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts - an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage 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 withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2020, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s Tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas due from others or Exchange gas due to others in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. 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."

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NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Deferred Charges in our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff.  These liabilities are classified as current or non-current according to when such amounts are expected to be recognized.  Current and non-current liabilities are included within Accrued Liabilities and Other Non-current Liabilities, respectively, in our Balance Sheet.

Leases

We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 15 years, with one having a term of up to 38 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We used judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

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)

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NOTES TO FINANCIAL STATEMENTS

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, 2020, 2019, and 2018 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. The levelized period for the 15-year contracts ended September 30, 2018.

We recorded regulatory debits totaling $1.1 million in 2020 and 2019, and $2.3 million in 2018 in the accompanying Statement of Net Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Expansion 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 method of allocation. 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, 2020 and 2019 were $96.3 million and $90.9 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation has been reclassified and netted against the amount of the ARO regulatory asset.

Impairment of Long-lived Assets

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

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

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

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and 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 2020, $0.7 million for 2019, and $0.5 million for 2018. The allowance for equity funds was $0.4 million, $2.7 million, and $1.7 million for 2020, 2019, and 2018, respectively.

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NOTES TO FINANCIAL STATEMENTS

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts receivable are stated at the historical carrying amount net of reserves or write-offs. We estimate the reserves, considering current expected credit losses (as discussed below in Accounting Standards Issued and Adopted). We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. 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.

Materials and Supplies Inventory

All inventories are stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2020 and 2019.

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 7. Benefit Plans). 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.

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NOTES TO FINANCIAL STATEMENTS

Interest Payments

Cash payments for interest, net of interest capitalized, were $26.1 million in 2020, $26.2 million in 2019, and $25.4 million in 2018.

Accounting Standards Issued and Adopted

In June 2016, the Financial Accounting Standards Board issued Accounting Standards Update (ASU) 2016-13 “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 changed 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 are required to use a forward-looking “expected loss” model that generally will result in the earlier recognition of allowances for losses. We adopted ASU 2016-13 effective January 1, 2020, which primarily applied to our short-term trade receivables. There was no cumulative effect adjustment to retained earnings upon adoption.

The majority of our trade receivable balances are due within 30 days. We monitor the credit quality of our counterparties through review of collection trends, credit ratings, and other analysis, such as bankruptcy monitoring. Financial assets are evaluated as one pool. Changes in counterparty risk factors could lead to reassessment of the composition of our financial assets as one pool. We calculate our allowance for credit losses incorporating an aging method. In estimating our expected credit losses, we utilized historical loss rates over many years. Our expected credit loss estimate considered both internal and external forward-looking commodity price expectations, as well as counterparty credit ratings, and factors impacting their near-term liquidity.

Past due accounts are generally written off against the allowance for doubtful accounts only after all collection attempts have been exhausted. We do not have a material amount of significantly aged receivables at December 31, 2020.

2. REVENUE RECOGNITION

Revenue by Category

Our revenue disaggregation by major service line includes Natural gas transportation, Natural gas storage, and Other, which are separately presented on the Statement of Net Income.

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	554	$	—
Revenue recognized in excess of amounts invoiced	2,841		554
Balance at end of period	$	3,395	$	554

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	5,464	$	—
Recorded contract liabilities	—		5,464
Recognized in Revenue	(854)		—
Balance at end of period	$	4,610	$	5,464

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NOTES TO FINANCIAL STATEMENTS

Remaining Performance Obligations

Our remaining performance obligations primarily include reservation charges on contracted capacity on our firm transportation and storage contracts with customers. Amounts from certain contracts included in the table below, which are subject to the periodic review and approval by the FERC, reflect the rates for such services in our current FERC tariffs for the life of the related contracts; however, these rates may change based on future rate cases or settlements approved by the FERC and the amount and timing of these changes is not currently known. This table excludes the variable consideration component for commodity charges. Certain of our contracts contain evergreen provisions for periods beyond the initial term of the contract. The remaining performance obligations as of December 31, 2020, do not consider potential future performance obligations for which the renewal has not been exercised. The table below also does not include contracts with customers for which the underlying facilities have not received FERC authorization to be placed into service.

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2020.

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2021	$	938	$	422,298
2022	1,029		408,593
2023	1,120		365,882
2024	1,218		335,757
2025	305		332,389
Thereafter	—		2,659,570
Total	$	4,610	$	4,524,489

Accounts Receivable

Receivables from contracts with customers are included within Receivables - Trade and Receivables - Affiliated companies and receivables that are not related to contracts with customers are included within the balance of Receivables - Advances to affiliate and Receivables - Other in our Balance Sheet.

3. LEASES

We are a lessee through noncancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions.

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NOTES TO FINANCIAL STATEMENTS

Lessee Activities

	Twelve Months Ended December 31,
	2020			2019
	(Thousands)
Lease Cost:
Operating lease cost	$	2,075			$	2,234
Variable lease cost	1,122				1,107
Total lease cost	$	3,197			$	3,341
Cash paid for amounts included in the measurement of operating lease liabilities	$	2,500			$	2,064
	December 31,
	2020				2019
	(Thousands)
Other Information:
Right-of-use assets	$	10,692			$	18,101
Operating lease liabilities:
Current (included in Accrued liabilities - Other in our Balance Sheet)	$	2,022			$	1,356
Lease liability	$	8,341			$	16,823
Weighted-average remaining lease term - operating leases (years)	15				13
Weighted-average discount rate - operating leases	3.96		%		4.80		%

Prior to adopting ASU 2016-02 “Leases (Topic 842)”, which was effective January 1, 2019, total rent expense was $2.8 million in 2018 and primarily included in Operation and maintenance and Administrative and general expenses in the Statement of Net Income.

As of December 31, 2020, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2021	$	2,315
2022	993
2023	911
2024	911
2025	927
Thereafter	8,474
Total future lease payments	14,531
Less amount representing interest	4,168
Total obligations under operating leases	$	10,363

4. RATE AND REGULATORY MATTERS

FERC Developments

Notice of Inquiry (Docket No. PL19-4-000). On May 21, 2020, the FERC issued a “Policy Statement on Determining Return on Equity for Natural Gas and Oil Pipelines” (Policy Statement) in Docket No. PL19-4-000 adopting changes to its policies concerning the calculation of a public utility return on equity (ROE). In this Policy Statement, the FERC revised its ROE policy for natural gas pipelines and oil pipelines to provide that the FERC will determine a pipeline’s ROE by averaging the results of the Discounted Cash Flow model and the Capital Asset Pricing Model, with each weighted equally. The FERC declined to adopt any additional policy changes at this time and will address all other issues concerning the determination of a pipeline’s ROE as they arise in future proceedings.

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NOTES TO FINANCIAL STATEMENTS

Our next general rate case must be filed for new rates to become effective no later than January 1, 2023.

5. 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 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, 2020, all of the meter stations have been remediated. During 2006 to 2018, 14 compressor stations were evaluated, of which 11 required remediation. As of December 31, 2020, 10 compressor stations have been remediated. At December 31, 2020 we had accrued liabilities totaling approximately $1.1 million, $0.1 million in current liabilities and $1.0 million in other non-current liabilities and at December 31, 2019 approximately $1.2 million, $0.1 million in current liabilities and $1.1 million in other non-current 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. These rulemakings include, but are not limited to, rules for reciprocating internal combustion engine and combustion turbine 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. The EPA previously issued its rule regarding National Ambient Air Quality Standards for ground-level ozone. We are monitoring the rule’s implementation as it 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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NOTES TO FINANCIAL STATEMENTS

6. DEBT AND FINANCING ARRANGEMENTS

Long-Term Debt

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

	December 31,
	2020		2019
	(Thousands)
7.125% unsecured debentures due 2025	$	85,000	$	85,000
4.0% unsecured debentures due 2027	500,000		500,000
Unamortized debt issuance costs	(3,581)		(4,083)
Unamortized debt discount	(3,401)		(3,872)
Total long-term debt	$	578,018	$	577,045

As of December 31, 2020, maturities of outstanding long-term debt (at face value) for the next five years are as follows:

	(Thousands)
7.125% unsecured debentures due 2025	$	85,000
Total	$	85,000

There are no maturities applicable to long-term debt outstanding for the years 2021, 2022, 2023 and 2024.

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

Restrictive Debt Covenants

At December 31, 2020, 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.

Credit Facility

In 2018, we, along with Williams and Transco (the borrowers), the lenders named therein, and an administrative agent entered into a credit agreement (Credit Agreement) with aggregate commitments available of $4.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. We and Transco are each subject to a $500 million borrowing sublimit. The facility made available under the Credit Agreement is initially available for five years from the Credit Agreement Effective Date (the Maturity Date). The borrowers may request an extension of the Maturity Date for an additional one-year period up to two times, to allow a Maturity Date as late as the seventh anniversary of the Credit Agreement Effective Date, subject to certain conditions. The Credit Agreement allows for same day swingline borrowings up to an aggregate amount of $200 million, subject to other utilization of the aggregate commitments under the Credit Agreement. Letter of credit commitments of $1.0 billion are, subject to the $500 million borrowing sublimit applicable to us and Transco, available to the borrowers. At December 31, 2020, no letters of credit have been issued and no loans to Williams were outstanding under the credit facility.

Measured as of December 31, 2020, 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.

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NOTES TO FINANCIAL STATEMENTS

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 applicable borrower may choose from two methods of calculating interest: a fluctuating base rate equal to Citibank N.A.'s alternate base rate plus an applicable margin or a periodic fixed rate equal to the London Interbank Offered Rate plus an applicable margin. We are required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin and the commitment fee are determined by reference to a pricing schedule based on the applicable borrower's senior unsecured long-term debt ratings.

Williams participates in a commercial paper program, and Williams 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 $4.0 billion of unsecured commercial paper notes. At December 31, 2020, Williams had no outstanding commercial paper.

7. 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 9. Transactions With Major Customers and Affiliates).

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 costs charged to us by Williams were $1.9 million in 2020, $2.2 million in 2019 and $3.9 million in 2018. Included in our pension costs are settlement charges of $0.7 million and $1.3 million in 2020 and 2018, respectively.

Williams provides subsidized retiree health care and life insurance benefits to certain eligible participants. Generally, participants that were employed by Williams on or before December 31, 1991 are eligible for subsidized retiree health care benefits. During 2020, 2019, and 2018, we received credits from Williams related to retiree health care and life insurance benefits of $1.7 million, $1.5 million and $2.1 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 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. The amounts of other postretirement benefits costs deferred as regulatory liabilities at December 31, 2020 and 2019 are $39.4 million and $37.7 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $2.3 million in 2020, $1.8 million in 2019 and $1.9 million in 2018 for Williams’ company 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, 2020, 2019 and 2018 was $1.3 million, $1.5 million and $1.8 million, respectively, excluding amounts allocated from WPZ and Williams.

8. 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 $578.0 million and $680.6 million, respectively, at December 31, 2020, and $577.0 million and $637.8 million, respectively, at December 31, 2019.

9. TRANSACTIONS WITH MAJOR CUSTOMERS AND AFFILIATES

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,
	2020		2019		2018
	(Thousands)
Puget Sound Energy, Inc.	$	132,747	$	121,792	$	115,238
Northwest Natural Gas Company	48,893		48,891		49,126
Cascade Natural Gas Corporation	47,493		46,969		46,164

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 Williams’ cash management program. At December 31, 2020 and 2019, the advances due to us by Williams totaled approximately $247.9 million and $201.3 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate in the accompanying Balance Sheet. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on Williams’ excess cash at the end of each month, which was approximately 0.01 percent at December 31, 2020. The interest income from these advances was $0.6 million, $4.1 million, and $2.0 million for the years ended December 31, 2020, 2019, and 2018, respectively. Such interest income is included in Other (Income) and Other Expenses: Miscellaneous other (income) expenses, net on the accompanying Statement of Net 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 $82.7 million, $96.2

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NOTES TO FINANCIAL STATEMENTS

million, and $92.7 million in the years ended December 31, 2020, 2019, and 2018, respectively, for these services. Such expenses are primarily included in General and administrative and Operation and maintenance expenses on the accompanying Statement of Net Income.

During 2020, 2019, and 2018, we declared and paid cash distributions to our parent of $164.0 million, $110.0 million, and $174.0 million, respectively. During February 2021, we declared and paid cash distributions of $55.0 million to our parent.

10. 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 2020 and 2019, our overall asset retirement obligation changed as follows (in thousands):

	2020		2019
Beginning balance	$	91,251	$	69,350
Accretion	5,410		4,605
Changes in estimates of existing obligations (1)	(884)		17,307
Property dispositions/obligations settled	—		(11)
Ending balance	$	95,777	$	91,251

(1)Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets. The decrease in 2020 is primarily due to a decrease in the inflation rate and an increase in the estimated remaining life of the ARO assets.

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NOTES TO FINANCIAL STATEMENTS

11. REGULATORY ASSETS AND LIABILITIES

Our regulatory assets and liabilities result from our application of the provisions of ASC Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Prepayments and other. Current regulatory liabilities are included in Exchange gas due to others. 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, 2020 and 2019:

	2020		2019
	(Thousands)
Current regulatory assets:
Levelized depreciation	$	1,360	$	978
Fuel Recovery	52		—
Total current regulatory assets	1,412		978
Non-current regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	5,114		5,498
Levelized depreciation	14,908		16,437
Total non-current regulatory assets	20,022		21,935
Total regulatory assets	$	21,434	$	22,913
Current regulatory liabilities:
Fuel recovery	$	3,232	$	4,121
Non-current regulatory liabilities:
Postretirement benefits	39,391		37,722
Deferred federal taxes-liability	206,527		206,527
Deferred state taxes - liability	12,120		12,120
Customer tax refund	75,694		49,598
Asset retirement obligations, net	21,993		17,065
Total non-current regulatory liabilities	355,725		323,032
Total regulatory liabilities	$	358,957	$	327,153

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.

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.

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.

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

43

NORTHWEST PIPELINE LLC

NOTES TO FINANCIAL STATEMENTS

adjustments. These amounts are not included in the rate base, and we are not currently recovering postretirement benefit costs in our rates (See Note 7. Benefit Plans).

Deferred Federal Taxes-Liability This 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.

Deferred State Taxes-Liability This regulatory liability balance, following the WPZ Merger, reflects a decrease to rate base deferred taxes due to a decrease to the estimated effective state income tax rates. 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.

Customer Tax Refund In our 2017 Settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates decreased due to subsequent legislation, such as Tax Reform enacted in 2017, we would record a regulatory liability. As a result of Tax Reform, the regulatory liability will be $23.6 million annually plus accrued interest ($5.0 million at December 31, 2020) for the period beginning January 1, 2018 and continuing through the time that our current rates remain effective.

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. AROs are expected to be fully recovered through the net negative salvage component of depreciation included in our rates (See Note 10. Asset Retirement Obligations).

44

Item 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE

None.

Item 9A. Controls and Procedures

Disclosure Controls and Procedures

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

Evaluation of Disclosure Controls and Procedures

An evaluation of the effectiveness of the design and operation of our Disclosure Controls was performed as of the end of the period covered by this report. This evaluation was performed under the supervision and with the participation of our management, including our Senior Vice President and our Vice President and Chief Accounting Officer. Based upon that evaluation, our Senior Vice President 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 2020 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 and our Vice President and Chief Accounting Officer, we assessed the effectiveness of our internal control over financial reporting as of

45

December 31, 2020, 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, 2020, our internal control over financial reporting was effective.

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.

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:

	2020		2019
	(Millions)
Audit fees	$	0.6	$	0.6
Audit related fees	—		—
Tax fees	—		—
All other fees	—		—
	$	0.6	$	0.6

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 Williams, we do not have a separate audit committee.  The Williams Audit Committee is responsible for the appointment, compensation, retention, and oversight of Ernst & Young LLP (“EY”) as such appointment relates to us and Williams’ other affiliates. The Williams Audit Committee is responsible for overseeing the determination of fees associated with EY’s audit of our financial statements. The Williams Audit Committee has established a policy regarding pre-approval of all audit and non-audit services provided by EY to Williams and its affiliates. On an ongoing basis, management presents specific projects and categories of service, including projects and categories of service relating to us, to the Williams Audit Committee to request advance approval. The Williams Audit Committee reviews those requests and advises management if the Williams Audit Committee approves the engagement of EY. On a periodic basis, management reports to the Williams Audit Committee regarding the actual spending for such projects and services compared to the approved amounts. The Williams Audit Committee may also delegate the authority to pre-approve audit and permitted non-audit services, excluding services related to internal control over financial reporting, to a subcommittee of one or more committee members, provided that any such pre-approvals are reported on at a subsequent Williams Audit Committee meeting.

46

PART IV

Item 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

	Page Reference to 2020 Form 10-K
(a) 1. and 2. Northwest Pipeline LLC financials
Index
Covered by reports of independent auditors:
Statement of Net Income for the Years Ended December 31, 2020, 2019, and 2018	25
Balance Sheet at December 31, 2020 and 2019	26
Statement of Member’s Equity for the Years Ended December 31, 2020, 2019, and 2018	28
Statement of Cash Flows for the Years Ended December 31, 2020, 2019, and 2018	29
Notes to Financial Statements	30

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.

47

(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 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	Credit Agreement dated as of July 13, 2018, between The Williams Companies, Inc., 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 July 17, 2018 as Exhibit 10.1 to The Williams Companies, Inc.’s Current Report on Form 8-K (File No. 001-04174) and incorporated herein by reference).
31.1*	Certification of Principal Executive Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended and Item 601(b)(31) of Regulation S-K, as adopted pursuant to Section 302 of The Sarbanes-Oxley Act of 2002.
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. The instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the inline XBRL document.
101.SCH*	XBRL Taxonomy Extension Schema.
101.CAL*	XBRL Taxonomy Extension Calculation Linkbase.
101.DEF*	XBRL Taxonomy Definition Linkbase
101.LAB*	XBRL Taxonomy Extension Label Linkbase.
101.PRE*	XBRL Taxonomy Extension Presentation Linkbase.
104*	Cover Page Interactive Data File. The cover page interactive data file does not appear in the interactive data file because its XBRL tags are embedded within the inline XBRL document (contained in Exhibit 101).

* Filed herewith

** Furnished herewith

Item 16. FORM 10-K SUMMARY

Not applicable.

48

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/ Billeigh W. Mark
	Billeigh W. Mark
	Controller
	(Principal Accounting Officer)

Date: February 24, 2021

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/ Scott A. Hallam	Management Committee Member and Senior Vice President (Principal Executive Officer)
Scott A. Hallam
/s/ John D. Porter	Vice President and Chief Accounting Officer (Principal Financial Officer)
John D. Porter
/s/ Billeigh W. Mark	Controller
Billeigh W. Mark	(Principal Accounting Officer)

Date: February 24, 2021

EX-31.1

Exhibit 31.1

SECTION 302 CERTIFICATION

I, Scott A. Hallam, 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 24, 2021

By:	/s/ Scott A. Hallam
	Scott A. Hallam
	Senior Vice President
	(Principal Executive Officer)

EX-31.2

Exhibit 31.2

SECTION 302 CERTIFICATION

I, John D. Porter, 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 24, 2021

By:	/s/ John D. Porter
	John D. Porter
	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, 2020 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/ Scott A. Hallam

Scott A. Hallam

Senior Vice President

February 24, 2021

/s/ John D. Porter

John D. Porter

Vice President and Chief Accounting Officer

February 24, 2021

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 - shares	12 Months Ended
	Dec. 31, 2020	Feb. 24, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-7414
Entity Registrant Name	NORTHWEST PIPELINE LLC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1157701
Entity Address, Address Line One	295 Chipeta Way
Entity Address, City or Town	Salt Lake City
Entity Address, State or Province	UT
Entity Address, Postal Zip Code	84108
City Area Code	801
Local Phone Number	583-8800
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0000110019
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		0

XML

Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenue
Natural gas transportation	$ 435,238	$ 428,656	$ 430,730
Natural gas storage	14,268	15,975	12,852
Other	(24)	(209)	36
Total operating revenues	449,482	444,422	443,618
OPERATING EXPENSES:
General and administrative	47,695	51,665	50,653
Operation and maintenance	69,970	81,736	75,237
Depreciation and amortization	112,004	107,951	106,073
Regulatory debits	1,148	1,107	2,334
Taxes, other than income taxes	16,290	14,388	17,507
Regulatory charges resulting from tax rate changes	23,580	23,580	35,680
Other expenses, net	(38)	47	444
Costs and Expenses	270,649	280,474	287,928
OPERATING INCOME	178,833	163,948	155,690
OTHER (INCOME) AND OTHER EXPENSES:
Interest expense	29,712	29,232	27,987
Allowance for equity and borrowed funds used during construction	(669)	(3,418)	(2,183)
Miscellaneous other (income) expenses, net	(1,296)	(4,533)	(1,575)
Total other (income) and other expenses	27,747	21,281	24,229
NET INCOME	$ 151,086	$ 142,667	$ 131,461

XML

Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Taxes, other than income taxes	$ 10,905	$ 9,913
CURRENT ASSETS:
Cash	0	0
Receivables:
Trade	37,365	40,066
Affiliated companies	51	109
Advances to affiliate	247,869	201,265
Other	840	1,962
Materials and supplies	9,807	9,683
Exchange gas due from others	4,466	5,534
Prepayments and other	4,078	3,346
Total current assets	304,476	261,965
PROPERTY, PLANT AND EQUIPMENT, at cost	3,653,792	3,593,186
Less-Accumulated depreciation	1,761,229	1,673,315
Total property, plant and equipment, net	1,892,563	1,919,871
OTHER ASSETS:
Deferred charges	3,775	1,075
Regulatory assets	20,022	21,935
Right-of-use assets	10,692	18,101
Total other assets	34,489	41,111
Total assets	2,231,528	2,222,947
Payables:
Trade	16,157	15,635
Affiliated companies	4,110	9,172
Accrued liabilities:
Taxes, other than income taxes	10,905	9,913
Interest	5,505	5,505
Exchange gas due to others	4,557	4,468
Customer advances	539	4,109
Other	6,786	6,990
Total current liabilities	48,559	55,792
LONG-TERM DEBT	578,018	577,045
OTHER NONCURRENT LIABILITIES:
Asset retirement obligations	95,777	91,251
Regulatory liabilities	355,725	323,032
Lease liability	8,341	16,823
Other	4,713	5,695
Total other noncurrent liabilities	464,556	436,801
MEMBER'S EQUITY:
Member's capital	1,073,892	1,073,892
Retained earnings	66,503	79,417
Total member's equity	1,140,395	1,153,309
Total liabilities and member's equity	$ 2,231,528	$ 2,222,947

XML

Statement of Member's Equity Statement of Member's Equity - USD ($) $ in Thousands	Total	MEMBER'S CAPITAL	RETAINED EARINGS
Balance at beginning of period at Dec. 31, 2017		$ 1,073,892	$ 89,289
Net income	$ 131,461		131,461
Cash distributions to parent	(174,000)		(174,000)
Balance at end of period at Dec. 31, 2018	1,120,642	1,073,892	46,750
Net income	142,667		142,667
Cash distributions to parent	(110,000)		(110,000)
Balance at end of period at Dec. 31, 2019	1,153,309	$ 1,073,892	79,417
Net income	151,086		151,086
Cash distributions to parent	(164,000)		(164,000)
Balance at end of period at Dec. 31, 2020	$ 1,140,395		$ 66,503

XML

Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES:
Net income	$ 151,086	$ 142,667	$ 131,461
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	112,004	107,951	106,073
Regulatory debits	1,148	1,107	2,334
Regulatory charges resulting from tax rate changes	23,580	23,580	35,680
Amortization of deferred charges and credits	(3,526)	(2,806)	954
Allowance for equity funds used during construction (equity AFUDC)	(414)	(2,744)	(1,703)
Changes in current assets and liabilities:
Trade and other accounts receivable	3,606	(1,528)	(1,611)
Affiliated receivables	58	(91)	1,903
Materials and supplies	(124)	363	39
Other current assets	337	4,311	4,494
Trade accounts payable	5,140	(1,497)	1,753
Affiliated payables	(5,062)	(17,360)	15,234
Other accrued liabilities	(8,603)	(8,056)	881
Changes in noncurrent assets and liabilities:
Regulatory liabilities	4,185	3,493	2,530
Other, net	503	8,570	(4,894)
Net cash provided by operating activities	283,918	257,960	295,128
FINANCING ACTIVITIES:
Proceeds from long-term debt	0	0	246,395
Retirement of long-term debt	0	0	(250,000)
Payments for debt issuance costs	0	(59)	(2,498)
Cash distributions to parent	(164,000)	(110,000)	(174,000)
Net cash used in financing activities	(164,000)	(110,059)	(180,103)
Property, plant and equipment:
Capital expenditures	(78,497)	(128,440)	(73,487)
Contributions and advances for construction costs	6,103	4,805	2,075
Disposal of property, plant and equipment, net	(920)	(3,401)	(879)
Advances to affiliates, net	(46,604)	(20,865)	(42,734)
Net cash used in investing activities	(119,918)	(147,901)	(115,025)
NET (DECREASE) INCREASE IN CASH	0	0	0
CASH AT BEGINNING OF PERIOD	0	0	0
CASH AT END OF PERIOD	0	0	0
Supplemental Cash Flow Elements [Abstract]
Increases to property, plant and equipment, exclusive of equity AFUDC	(78,602)	(132,260)	(73,105)
Changes in related accounts receivable, accounts payable, and accrued liabilities	105	3,820	(382)
Capital expenditures	$ (78,497)	$ (128,440)	$ (73,487)

XML

Summary of Significant Accounting Policies (Notes)

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Significant Accounting Policies

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Corporate Structure and Control

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

Northwest Pipeline LLC (Northwest) was indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which was consolidated by The Williams Companies, Inc. (Williams). On August 10, 2018, Williams completed a merger with WPZ, pursuant to which Williams acquired all of the publicly held outstanding common units of WPZ in exchange for shares of Williams’ common stock (WPZ Merger). Williams continued as the surviving entity. Northwest is now indirectly owned by Williams.

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

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). Accounting Standards Codification (ASC) Regulated Operations, (Topic 980) provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. 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.

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; 5) asset retirement obligations; and 6) regulatory deferred tax.

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipelines business and are not within the scope of Accounting Standards Update (ASU) 2014-09, Revenues from Contracts with Customers (ASC 606). Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed assets.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Most of our firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas scheduled, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended beyond the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts - an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts - an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage 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 withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2020, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s Tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas due from others or Exchange gas due to others in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. 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."

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Deferred Charges in our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff.  These liabilities are classified as current or non-current according to when such amounts are expected to be recognized.  Current and non-current liabilities are included within Accrued Liabilities and Other Non-current Liabilities, respectively, in our Balance Sheet.

Leases

We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 15 years, with one having a term of up to 38 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We used judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

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, 2020, 2019, and 2018 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. The levelized period for the 15-year contracts ended September 30, 2018.

We recorded regulatory debits totaling $1.1 million in 2020 and 2019, and $2.3 million in 2018 in the accompanying Statement of Net Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Expansion 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 method of allocation. 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, 2020 and 2019 were $96.3 million and $90.9 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation has been reclassified and netted against the amount of the ARO regulatory asset.

Impairment of Long-lived Assets

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

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

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

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and 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 2020, $0.7 million for 2019, and $0.5 million for 2018. The allowance for equity funds was $0.4 million, $2.7 million, and $1.7 million for 2020, 2019, and 2018, respectively.

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts receivable are stated at the historical carrying amount net of reserves or write-offs. We estimate the reserves, considering current expected credit losses (as discussed below in Accounting Standards Issued and Adopted). We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. 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.

Materials and Supplies Inventory

All inventories are stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2020 and 2019.

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 7. Benefit Plans). 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 $26.1 million in 2020, $26.2 million in 2019, and $25.4 million in 2018.

Accounting Standards Issued and Adopted

In June 2016, the Financial Accounting Standards Board issued Accounting Standards Update (ASU) 2016-13 “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 changed 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 are required to use a forward-looking “expected loss” model that generally will result in the earlier recognition of allowances for losses. We adopted ASU 2016-13 effective January 1, 2020, which primarily applied to our short-term trade receivables. There was no cumulative effect adjustment to retained earnings upon adoption.

The majority of our trade receivable balances are due within 30 days. We monitor the credit quality of our counterparties through review of collection trends, credit ratings, and other analysis, such as bankruptcy monitoring. Financial assets are evaluated as one pool. Changes in counterparty risk factors could lead to reassessment of the composition of our financial assets as one pool. We calculate our allowance for credit losses incorporating an aging method. In estimating our expected credit losses, we utilized historical loss rates over many years. Our expected credit loss estimate considered both internal and external forward-looking commodity price expectations, as well as counterparty credit ratings, and factors impacting their near-term liquidity.

Past due accounts are generally written off against the allowance for doubtful accounts only after all collection attempts have been exhausted. We do not have a material amount of significantly aged receivables at December 31, 2020.

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Revenue Recognition Revenue Recognition (Notes)

12 Months Ended

Dec. 31, 2020

Revenue Recognition [Abstract]

Revenue from Contract with Customer [Text Block]

REVENUE RECOGNITION

Revenue by Category

Our revenue disaggregation by major service line includes Natural gas transportation, Natural gas storage, and Other, which are separately presented on the Statement of Net Income.

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	554	$	—
Revenue recognized in excess of amounts invoiced	2,841		554
Balance at end of period	$	3,395	$	554

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	5,464	$	—
Recorded contract liabilities	—		5,464
Recognized in Revenue	(854)		—
Balance at end of period	$	4,610	$	5,464

Remaining Performance Obligations

Our remaining performance obligations primarily include reservation charges on contracted capacity on our firm transportation and storage contracts with customers. Amounts from certain contracts included in the table below, which are subject to the periodic review and approval by the FERC, reflect the rates for such services in our current FERC tariffs for the life of the related contracts; however, these rates may change based on future rate cases or settlements approved by the FERC and the amount and timing of these changes is not currently known. This table excludes the variable consideration component for commodity charges. Certain of our contracts contain evergreen provisions for periods beyond the initial term of the contract. The remaining performance obligations as of December 31, 2020, do not consider potential future performance obligations for which the renewal has not been exercised. The table below also does not include contracts with customers for which the underlying facilities have not received FERC authorization to be placed into service.

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2020.

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2021	$	938	$	422,298
2022	1,029		408,593
2023	1,120		365,882
2024	1,218		335,757
2025	305		332,389
Thereafter	—		2,659,570
Total	$	4,610	$	4,524,489

Accounts Receivable

Receivables from contracts with customers are included within Receivables - Trade and Receivables - Affiliated companies and receivables that are not related to contracts with customers are included within the balance of Receivables - Advances to affiliate and Receivables - Other in our Balance Sheet.

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Leases (Notes)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Leases of Lessee Disclosure [Text Block]

LEASES We are a lessee through noncancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions.

Lessee Activities

	Twelve Months Ended December 31,
	2020			2019
	(Thousands)
Lease Cost:
Operating lease cost	$	2,075			$	2,234
Variable lease cost	1,122				1,107
Total lease cost	$	3,197			$	3,341
Cash paid for amounts included in the measurement of operating lease liabilities	$	2,500			$	2,064
	December 31,
	2020				2019
	(Thousands)
Other Information:
Right-of-use assets	$	10,692			$	18,101
Operating lease liabilities:
Current (included in Accrued liabilities - Other in our Balance Sheet)	$	2,022			$	1,356
Lease liability	$	8,341			$	16,823
Weighted-average remaining lease term - operating leases (years)	15				13
Weighted-average discount rate - operating leases	3.96		%		4.80		%

Prior to adopting ASU 2016-02 “Leases (Topic 842)”, which was effective January 1, 2019, total rent expense was $2.8 million in 2018 and primarily included in Operation and maintenance and Administrative and general expenses in the Statement of Net Income.

As of December 31, 2020, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2021	$	2,315
2022	993
2023	911
2024	911
2025	927
Thereafter	8,474
Total future lease payments	14,531
Less amount representing interest	4,168
Total obligations under operating leases	$	10,363

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Rate and Regulatory Matters (Notes)

12 Months Ended

Dec. 31, 2020

Public Utilities, Rate Matters [Abstract]

Public Utilities, Disclosure of Rate Matters [Text Block]

RATE AND REGULATORY MATTERS

FERC Developments

Notice of Inquiry (Docket No. PL19-4-000). On May 21, 2020, the FERC issued a “Policy Statement on Determining Return on Equity for Natural Gas and Oil Pipelines” (Policy Statement) in Docket No. PL19-4-000 adopting changes to its policies concerning the calculation of a public utility return on equity (ROE). In this Policy Statement, the FERC revised its ROE policy for natural gas pipelines and oil pipelines to provide that the FERC will determine a pipeline’s ROE by averaging the results of the Discounted Cash Flow model and the Capital Asset Pricing Model, with each weighted equally. The FERC declined to adopt any additional policy changes at this time and will address all other issues concerning the determination of a pipeline’s ROE as they arise in future proceedings.

Our next general rate case must be filed for new rates to become effective no later than January 1, 2023.

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Contingent Liabilities and Commitments (Notes)

12 Months Ended

Dec. 31, 2020

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 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, 2020, all of the meter stations have been remediated. During 2006 to 2018, 14 compressor stations were evaluated, of which 11 required remediation. As of December 31, 2020, 10 compressor stations have been remediated. At December 31, 2020 we had accrued liabilities totaling approximately $1.1 million, $0.1 million in current liabilities and $1.0 million in other non-current liabilities and at December 31, 2019 approximately $1.2 million, $0.1 million in current liabilities and $1.1 million in other non-current 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. These rulemakings include, but are not limited to, rules for reciprocating internal combustion engine and combustion turbine 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. The EPA previously issued its rule regarding National Ambient Air Quality Standards for ground-level ozone. We are monitoring the rule’s implementation as it 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, 2020

Debt Disclosure [Abstract]

Debt Disclosure

DEBT AND FINANCING ARRANGEMENTS

Long-Term Debt

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

	December 31,
	2020		2019
	(Thousands)
7.125% unsecured debentures due 2025	$	85,000	$	85,000
4.0% unsecured debentures due 2027	500,000		500,000
Unamortized debt issuance costs	(3,581)		(4,083)
Unamortized debt discount	(3,401)		(3,872)
Total long-term debt	$	578,018	$	577,045

As of December 31, 2020, maturities of outstanding long-term debt (at face value) for the next five years are as follows:

	(Thousands)
7.125% unsecured debentures due 2025	$	85,000
Total	$	85,000

There are no maturities applicable to long-term debt outstanding for the years 2021, 2022, 2023 and 2024.

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

Restrictive Debt Covenants

At December 31, 2020, 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.

Credit Facility

In 2018, we, along with Williams and Transco (the borrowers), the lenders named therein, and an administrative agent entered into a credit agreement (Credit Agreement) with aggregate commitments available of $4.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. We and Transco are each subject to a $500 million borrowing sublimit. The facility made available under the Credit Agreement is initially available for five years from the Credit Agreement Effective Date (the Maturity Date). The borrowers may request an extension of the Maturity Date for an additional one-year period up to two times, to allow a Maturity Date as late as the seventh anniversary of the Credit Agreement Effective Date, subject to certain conditions. The Credit Agreement allows for same day swingline borrowings up to an aggregate amount of $200 million, subject to other utilization of the aggregate commitments under the Credit Agreement. Letter of credit commitments of $1.0 billion are, subject to the $500 million borrowing sublimit applicable to us and Transco, available to the borrowers. At December 31, 2020, no letters of credit have been issued and no loans to Williams were outstanding under the credit facility.

Measured as of December 31, 2020, 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 applicable borrower may choose from two methods of calculating interest: a fluctuating base rate equal to Citibank N.A.'s alternate base rate plus an applicable margin or a periodic fixed rate equal to the London Interbank Offered Rate plus an applicable margin. We are required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin and the commitment fee are determined by reference to a pricing schedule based on the applicable borrower's senior unsecured long-term debt ratings.

Williams participates in a commercial paper program, and Williams 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 $4.0 billion of unsecured commercial paper notes. At December 31, 2020, Williams had no outstanding commercial paper.

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Employee Benefit Plans (Notes)

12 Months Ended

Dec. 31, 2020

Retirement Benefits [Abstract]

Employee Benefit Plans [Text Block]

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 9. Transactions With Major Customers and Affiliates).

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 costs charged to us by Williams were $1.9 million in 2020, $2.2 million in 2019 and $3.9 million in 2018. Included in our pension costs are settlement charges of $0.7 million and $1.3 million in 2020 and 2018, respectively.

Williams provides subsidized retiree health care and life insurance benefits to certain eligible participants. Generally, participants that were employed by Williams on or before December 31, 1991 are eligible for subsidized retiree health care benefits. During 2020, 2019, and 2018, we received credits from Williams related to retiree health care and life insurance benefits of $1.7 million, $1.5 million and $2.1 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 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. The amounts of other postretirement benefits costs deferred as regulatory liabilities at December 31, 2020 and 2019 are $39.4 million and $37.7 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $2.3 million in 2020, $1.8 million in 2019 and $1.9 million in 2018 for Williams’ company 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, 2020, 2019 and 2018 was $1.3 million, $1.5 million and $1.8 million, respectively, excluding amounts allocated from WPZ and Williams.

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Financial Instruments (Notes)

12 Months Ended

Dec. 31, 2020

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 $578.0 million and $680.6 million, respectively, at December 31, 2020, and $577.0 million and $637.8 million, respectively, at December 31, 2019.

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Transactions with Major Customers and Affiliates (Notes)

12 Months Ended

Dec. 31, 2020

Transactions with Major Customers and Affiliates [Abstract]

Transactions with Major Customers and Affiliates

TRANSACTIONS WITH MAJOR CUSTOMERS AND AFFILIATES

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,
	2020		2019		2018
	(Thousands)
Puget Sound Energy, Inc.	$	132,747	$	121,792	$	115,238
Northwest Natural Gas Company	48,893		48,891		49,126
Cascade Natural Gas Corporation	47,493		46,969		46,164

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 Williams’ cash management program. At December 31, 2020 and 2019, the advances due to us by Williams totaled approximately $247.9 million and $201.3 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate in the accompanying Balance Sheet. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on Williams’ excess cash at the end of each month, which was approximately 0.01 percent at December 31, 2020. The interest income from these advances was $0.6 million, $4.1 million, and $2.0 million for the years ended December 31, 2020, 2019, and 2018, respectively. Such interest income is included in Other (Income) and Other Expenses: Miscellaneous other (income) expenses, net on the accompanying Statement of Net 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 $82.7 million, $96.2

million, and $92.7 million in the years ended December 31, 2020, 2019, and 2018, respectively, for these services. Such expenses are primarily included in General and administrative and Operation and maintenance expenses on the accompanying Statement of Net Income.

During 2020, 2019, and 2018, we declared and paid cash distributions to our parent of $164.0 million, $110.0 million, and $174.0 million, respectively. During February 2021, we declared and paid cash distributions of $55.0 million to our parent.

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Asset Retirement Obligations (Notes)

12 Months Ended

Dec. 31, 2020

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 2020 and 2019, our overall asset retirement obligation changed as follows (in thousands):

	2020		2019
Beginning balance	$	91,251	$	69,350
Accretion	5,410		4,605
Changes in estimates of existing obligations (1)	(884)		17,307
Property dispositions/obligations settled	—		(11)
Ending balance	$	95,777	$	91,251

(1)Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets. The decrease in 2020 is primarily due to a decrease in the inflation rate and an increase in the estimated remaining life of the ARO assets.

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Regulatory Assets and Liabilities (Notes)

12 Months Ended

Dec. 31, 2020

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 ASC Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Prepayments and other. Current regulatory liabilities are included in Exchange gas due to others. 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, 2020 and 2019:

	2020		2019
	(Thousands)
Current regulatory assets:
Levelized depreciation	$	1,360	$	978
Fuel Recovery	52		—
Total current regulatory assets	1,412		978
Non-current regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	5,114		5,498
Levelized depreciation	14,908		16,437
Total non-current regulatory assets	20,022		21,935
Total regulatory assets	$	21,434	$	22,913
Current regulatory liabilities:
Fuel recovery	$	3,232	$	4,121
Non-current regulatory liabilities:
Postretirement benefits	39,391		37,722
Deferred federal taxes-liability	206,527		206,527
Deferred state taxes - liability	12,120		12,120
Customer tax refund	75,694		49,598
Asset retirement obligations, net	21,993		17,065
Total non-current regulatory liabilities	355,725		323,032
Total regulatory liabilities	$	358,957	$	327,153

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.

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.

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.

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 7. Benefit Plans).

Deferred Federal Taxes-Liability This 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.

Deferred State Taxes-Liability This regulatory liability balance, following the WPZ Merger, reflects a decrease to rate base deferred taxes due to a decrease to the estimated effective state income tax rates. 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.

Customer Tax Refund In our 2017 Settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates decreased due to subsequent legislation, such as Tax Reform enacted in 2017, we would record a regulatory liability. As a result of Tax Reform, the regulatory liability will be $23.6 million annually plus accrued interest ($5.0 million at December 31, 2020) for the period beginning January 1, 2018 and continuing through the time that our current rates remain effective.

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. AROs are expected to be fully recovered through the net negative salvage component of depreciation included in our rates (See Note 10. Asset Retirement Obligations).

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Summary of Significant Accounting Policies (Policies) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Regulatory Accounting

Regulatory AccountingWe are regulated by the Federal Energy Regulatory Commission (FERC). Accounting Standards Codification (ASC) Regulated Operations, (Topic 980) provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. 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.

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; 5) asset retirement obligations; and 6) regulatory deferred tax.

Revenue Recognition

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipelines business and are not within the scope of Accounting Standards Update (ASU) 2014-09, Revenues from Contracts with Customers (ASC 606). Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed assets.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Most of our firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas scheduled, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended beyond the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts - an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts - an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage 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 withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2020, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s Tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas due from others or Exchange gas due to others in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. 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."

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Deferred Charges in our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff.  These liabilities are classified as current or non-current according to when such amounts are expected to be recognized.  Current and non-current liabilities are included within Accrued Liabilities and Other Non-current Liabilities, respectively, in our Balance Sheet.

Leases

Leases

We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 15 years, with one having a term of up to 38 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We used judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

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, 2020, 2019, and 2018 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. The levelized period for the 15-year contracts ended September 30, 2018.

We recorded regulatory debits totaling $1.1 million in 2020 and 2019, and $2.3 million in 2018 in the accompanying Statement of Net Income. These debits relate primarily to the levelized depreciation adjustment for the Evergreen Expansion 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 method of allocation. 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, 2020 and 2019 were $96.3 million and $90.9 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation 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 our long-lived assets, including capitalized project development costs, for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. When an indicator of a potential impairment has occurred, we compare our management’s estimate of undiscounted future cash flows attributable to the assets to the carrying value of the assets to determine whether an impairment has occurred. We apply a probability-weighted approach to consider the likelihood of different cash flow assumptions. If an impairment of the carrying value has occurred, we determine the amount of the impairment recognized in the financial statements by estimating the fair value of the assets and recording a loss for the amount that the carrying value exceeds the estimated fair value.

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

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

Allowance for Funds Used During Construction

Allowance for Funds Used During ConstructionAllowance 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 2020, $0.7 million for 2019, and $0.5 million for 2018. The allowance for equity funds was $0.4 million, $2.7 million, and $1.7 million for 2020, 2019, and 2018, respectively.

Income Taxes

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

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. We estimate the reserves, considering current expected credit losses (as discussed below in Accounting Standards Issued and Adopted). We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. 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.

Materials and Supplies Inventory

Materials and Supplies Inventory

All inventories are stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. There was a minimal reserve at December 31, 2020 and 2019.

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 7. Benefit Plans). 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

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

$ 26.1

$ 26.2

$ 25.4

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Financial Instruments (Policies)

12 Months Ended

Dec. 31, 2020

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 $578.0 million and $680.6 million, respectively, at December 31, 2020, and $577.0 million and $637.8 million, respectively, at December 31, 2019.

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Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020, 2019, and 2018 are as follows:

Category of Property
Storage Facilities	1.60	%	—	2.76%
Transmission Facilities	2.80	%	—	6.97%

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Revenue Recognition Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2020

Revenue Recognition [Abstract]

Contract with Customer, Asset and Liability [Table Text Block]

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	554	$	—
Revenue recognized in excess of amounts invoiced	2,841		554
Balance at end of period	$	3,395	$	554

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year ended December 31,
	2020		2019
	(Thousands)
Balance at beginning of period	$	5,464	$	—
Recorded contract liabilities	—		5,464
Recognized in Revenue	(854)		—
Balance at end of period	$	4,610	$	5,464

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2020.

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2021	$	938	$	422,298
2022	1,029		408,593
2023	1,120		365,882
2024	1,218		335,757
2025	305		332,389
Thereafter	—		2,659,570
Total	$	4,610	$	4,524,489

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Leases Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Lease, Cost [Table Text Block]

	Twelve Months Ended December 31,
	2020			2019
	(Thousands)
Lease Cost:
Operating lease cost	$	2,075			$	2,234
Variable lease cost	1,122				1,107
Total lease cost	$	3,197			$	3,341
Cash paid for amounts included in the measurement of operating lease liabilities	$	2,500			$	2,064
	December 31,
	2020				2019
	(Thousands)
Other Information:
Right-of-use assets	$	10,692			$	18,101
Operating lease liabilities:
Current (included in Accrued liabilities - Other in our Balance Sheet)	$	2,022			$	1,356
Lease liability	$	8,341			$	16,823
Weighted-average remaining lease term - operating leases (years)	15				13
Weighted-average discount rate - operating leases	3.96		%		4.80		%

Lessee, Operating Lease, Liability, Maturity [Table Text Block]

As of December 31, 2020, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2021	$	2,315
2022	993
2023	911
2024	911
2025	927
Thereafter	8,474
Total future lease payments	14,531
Less amount representing interest	4,168
Total obligations under operating leases	$	10,363

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Debt, Financing Arrangements, and Leases (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Long-term debt

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

	December 31,
	2020		2019
	(Thousands)
7.125% unsecured debentures due 2025	$	85,000	$	85,000
4.0% unsecured debentures due 2027	500,000		500,000
Unamortized debt issuance costs	(3,581)		(4,083)
Unamortized debt discount	(3,401)		(3,872)
Total long-term debt	$	578,018	$	577,045

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Transactions with Major Customers and Affiliates (Tables)

12 Months Ended

Dec. 31, 2020

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,
	2020		2019		2018
	(Thousands)
Puget Sound Energy, Inc.	$	132,747	$	121,792	$	115,238
Northwest Natural Gas Company	48,893		48,891		49,126
Cascade Natural Gas Corporation	47,493		46,969		46,164

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Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2020

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2020 and 2019, our overall asset retirement obligation changed as follows (in thousands):

	2020		2019
Beginning balance	$	91,251	$	69,350
Accretion	5,410		4,605
Changes in estimates of existing obligations (1)	(884)		17,307
Property dispositions/obligations settled	—		(11)
Ending balance	$	95,777	$	91,251

(1)Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets. The decrease in 2020 is primarily due to a decrease in the inflation rate and an increase in the estimated remaining life of the ARO assets.

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Regulatory Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

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 ASC Topic 980 and are reflected on our Balance Sheet. Current regulatory assets are included in Prepayments and other. Current regulatory liabilities are included in Exchange gas due to others. 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, 2020 and 2019:

	2020		2019
	(Thousands)
Current regulatory assets:
Levelized depreciation	$	1,360	$	978
Fuel Recovery	52		—
Total current regulatory assets	1,412		978
Non-current regulatory assets:
Grossed-up deferred taxes on equity funds used during construction	5,114		5,498
Levelized depreciation	14,908		16,437
Total non-current regulatory assets	20,022		21,935
Total regulatory assets	$	21,434	$	22,913
Current regulatory liabilities:
Fuel recovery	$	3,232	$	4,121
Non-current regulatory liabilities:
Postretirement benefits	39,391		37,722
Deferred federal taxes-liability	206,527		206,527
Deferred state taxes - liability	12,120		12,120
Customer tax refund	75,694		49,598
Asset retirement obligations, net	21,993		17,065
Total non-current regulatory liabilities	355,725		323,032
Total regulatory liabilities	$	358,957	$	327,153

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Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Entity number of employees | employee	0
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	$ 21,434	$ 22,913
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, debt	300	700	$ 500
Allowance for funds used during construction, equity	400	2,700	1,700
Interest Payments [Abstract]
Cash payments for interest, net of interest capitalized	26,100	26,200	25,400
Levelized depreciation
Public Utility, Property, Plant and Equipment [Line Items]
regulatory debits	1,100	1,100	$ 2,300
Asset retirement obligation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	$ 96,300	$ 90,900
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%
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	38 years
Accounting Standards Update 2016-02 [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Accounting Standards Update 2016-02 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	15 years

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Revenue Recognition Revenue recognition contract liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue Recognition [Abstract]
Contract with Customer, Liability	$ 5,464	$ 0
Recognized in Revenue	0	5,464
Increase (Decrease) in Contract with Customer, Liability	(854)	0
Contract with Customer, Liability - End of Period	4,610	5,464
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	4,524,489
Revenue Recognition and Deferred Revenue [Abstract]
Contract with Customer, Asset, Net - Beginning of Period	554	0
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	2,841	554
Contract with Customer, Asset, Net - End of Period	3,395	$ 554
Revenue, Remaining Performance Obligation, Amount	4,524,489
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	938
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	1,029
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	1,120
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	1,218
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	305
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue Recognition [Abstract]
Contract with Customer, Liability - End of Period	0
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 422,298
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 422,298
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 408,593
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 408,593
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 365,882
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 365,882
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 335,757
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 335,757
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 332,389
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 332,389
Remaining Performance Obligations [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,659,570
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 2,659,570
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year

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Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 2,075	$ 2,234
Variable lease cost	1,122	1,107
Total lease cost	3,197	3,341
Cash paid for amounts included in the measurement of operating lease liabilities	2,500	2,064
Right-of-use assets	10,692	18,101
Lease liability	$ 8,341	$ 16,823
Weighted-average remaining lease term - operating lease	15 years	13 years
Weighted-average discount rate - operating lease	3.96%	4.80%
Prior to adopting ASU 2016-02, total rent expense			$ 2,800
2021	$ 2,315
2022	993
2023	911
2024	911
2025	927
Thereafter	8,474
Total future lease payments	14,531
Less amount representing interest	4,168
Total obligations under operating leases	10,363
Other Current Liabilities
Lessee, Lease, Description [Line Items]
Current (included in Other in our Balance Sheet	$ 2,022	$ 1,356

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Contingent Liabilities and Commitments (Details) - Environmental assessment and remediation - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	$ 1.1	$ 1.2
Accrued environmental assessment and remediation costs, current	0.1	0.1
Accrued environmental assessment and remediation costs, noncurrent	$ 1.0	$ 1.1

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Debt, Financing Arrangements, and Leases Debt Disclosure (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt	$ 578,018,000	$ 577,045,000
Debt issuance costs	(3,581,000)	(4,083,000)
Unamortized debt discount	(3,401,000)	(3,872,000)
Property pledged as collateral	0
Long-term Debt, Fiscal Year Maturity [Abstract]
2021	0
2022	0
2023	0
2024	0
2025	85,000,000
7.125 percent unsecured debentures due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	85,000,000	85,000,000
4.0% unsecured debentures due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 500,000,000	$ 500,000,000

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Debt, Financing Arrangements, and Leases Line of Credit Facility (Details) - USD ($)	Dec. 31, 2020	Jul. 13, 2018
Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Commercial paper, amount outstanding	$ 0
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 500,000,000
Line of Credit [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		4,500,000,000
Additional Amount By Which Credit Facility Can Be Increased		500,000,000
Long-term Line of Credit	0
Swing Line Loan | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		200,000,000
Commercial Paper [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		4,000,000,000.0
Letter of Credit [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,000,000,000.0
Letters of Credit Outstanding, Amount	$ 0

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Employee Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	$ (355,725)	$ (323,032)
Regulatory Liabilities	358,957	327,153
Salary and Wage, Excluding Cost of Good and Service Sold [Abstract]
Stock-based compensation expense	1,300	1,500	$ 1,800
Other Postretirement Benefit Costs
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	(39,400)	(37,700)
Williams Companies Inc [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension cost	1,900	2,200	3,900
Defined contribution plan matching contributions expense	2,300	1,800	1,900
Williams Companies Inc [Member] | Retiree health care and life insurance benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	(1,700)	$ (1,500)	(2,100)
Williams Companies Inc [Member] | Pension Plan [Member] | Directly charged [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension cost charges to us by Williams	$ 700		$ 1,300

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Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 578.0	$ 577.0
Estimate of fair value of long-term debt, including current maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 680.6	$ 637.8

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Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2021 USD ($)	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 247,869	$ 201,265
Related party transaction, rate		0.01%
Interest Income, affiliate		$ 600	4,100	$ 2,000
Entity number of employees | employee		0
Related party transaction, expenses from transactions with related party		$ 82,700	96,200	92,700
Cash distributions to parent		(164,000)	(110,000)	(174,000)
Williams Companies Inc [Member]
Related Party Transaction [Line Items]
Advances to affiliate		247,900	201,300
Cash distributions to parent		164,000	110,000	174,000
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 55,000
Puget Sound Energy, Inc.
Revenue, Major Customer [Line Items]
Operating revenues		132,747	121,792	115,238
Northwest Natural Gas Company
Revenue, Major Customer [Line Items]
Operating revenues		48,893	48,891	49,126
Cascade Natural Gas Corporation
Revenue, Major Customer [Line Items]
Operating revenues		$ 47,493	$ 46,969	$ 46,164

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Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 91,251	$ 69,350
Accretion	5,410	4,605
Changes in estimates of existing obligations (1)	(884)	17,307
Property dispositions/obligations settled	0	(11)
Ending balance	$ 95,777	$ 91,251

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Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Current regulatory assets	$ 1,412	$ 978
Regulatory assets, noncurrent	20,022	21,935
Total regulatory assets	21,434	22,913
Regulatory Liabilities [Line Items]
Regulatory liabilities	355,725	323,032
Total regulatory liabilities	358,957	327,153
Fuel recovery
Regulatory Liabilities [Line Items]
Current regulatory liabilities	3,232	4,121
Postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	39,391	37,722
Deferred federal taxes-liability
Regulatory Liabilities [Line Items]
Regulatory liabilities	206,527	206,527
Deferred state taxes - liability
Regulatory Liabilities [Line Items]
Regulatory liabilities	12,120	12,120
Customer tax refund [Domain]
Regulatory Liabilities [Line Items]
Regulatory liabilities	75,694	49,598
Asset retirement obligations, net [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21,993	17,065
Accrued Interest on Deferred Regulatory Tax Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	5,000
Regulatory charges resulting from tax rate changes [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23,600
Levelized depreciation
Regulatory Assets [Line Items]
Current regulatory assets	1,360	978
Regulatory assets, noncurrent	14,908	16,437
Fuel recovery
Regulatory Assets [Line Items]
Current regulatory assets	52	0
Grossed-up deferred taxes on equity funds used during construction
Regulatory Assets [Line Items]
Regulatory assets, noncurrent	$ 5,114	$ 5,498