Basis of Presentation (Notes)	3 Months Ended
Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	BASIS OF PRESENTATION Northwest Pipeline LLC (Northwest) is indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which is consolidated by The Williams Companies, Inc. (Williams). On February 2, 2015, WPZ was merged into Access Midstream Partners, L.P. (ACMP), another publicly traded limited partnership consolidated by Williams. ACMP was the surviving partnership and was subsequently renamed WPZ. At March 31, 2016, Williams holds an approximate 60 percent interest in WPZ, comprised of an approximate 58 percent limited partner interest and all of the 2 percent general partner interest. On September 28, 2015, Williams publicly announced in a press release that it had entered into an Agreement and Plan of Merger (Merger Agreement) with Energy Transfer Equity, L.P. (Energy Transfer) and certain of its affiliates. The Merger Agreement provides that, subject to the satisfaction of customary closing conditions, Williams will be merged with and into the newly formed Energy Transfer Corp LP (ETC) (ETC Merger) with ETC surviving the ETC Merger. Energy Transfer formed ETC as a limited partnership that will be treated as a corporation for U.S. federal income tax purposes. Immediately following the completion of the ETC Merger, ETC will contribute to Energy Transfer all of the assets and liabilities of Williams in exchange for the issuance by Energy Transfer to ETC of a number of Energy Transfer Class E common units equal to the number of ETC common shares issued to Williams stockholders in the ETC Merger. WPZ expects to retain its current name and remain a publicly traded limited partnership following the ETC Merger. In this report, Northwest is at times referred to in the first person as “we,” “us,” or “our.” General The accompanying interim financial statements do not include all the notes in our annual financial statements, and therefore, should be read in conjunction with the financial statements and notes thereto in our 2015 Annual Report on Form 10-K. The accompanying unaudited financial statements include all adjustments both normal recurring and others which, in the opinion of our management, are necessary to present fairly our interim financial statements. The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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. Accounting Standards Issued But Not Yet Adopted In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02 "Leases (Topic 842)" (ASU 2016-02). ASU 2016-02 establishes a comprehensive new lease accounting model. The new standard clarifies the definition of a lease, requires a dual approach to lease classification similar to current lease classifications, and causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset. The new standard is effective for interim and annual periods beginning after December 15, 2018. Early adoption is permitted. The new standard requires a modified retrospective transition for capital or operating leases existing at or entered into after the beginning of the earliest comparative period presented in the financial statements. We are evaluating the impact of the new standards on our financial statements. In May 2014, the FASB issued ASU 2014-09 establishing Accounting Standards Codification Topic 606, "Revenue from Contracts with Customers" (ASC 606). ASC 606 establishes a comprehensive new revenue recognition model designed to depict the transfer of goods or services to a customer in an amount that reflects the consideration the entity expects to be entitled to receive in exchange for those goods or services and requires significantly enhanced revenue disclosures. In April 2016, the FASB issued ASU 2016-10 "Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing" (ASU 2016-10) to clarify aspects of Topic 606 related to identifying performance obligations and licensing implementation guidance. In August 2015, the FASB issued ASU 2015-14 "Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date" (ASU 2015-14). Per ASU 2015-14, the standard is effective for interim and annual reporting periods beginning after December 15, 2017. ASC 606 allows either full retrospective or modified retrospective transition and early adoption is permitted for annual periods beginning after December 15, 2016. We continue to evaluate both the impact of this new standard on our financial statements and the transition method we will utilize for adoption.

BASIS OF PRESENTATION

Northwest Pipeline LLC (Northwest) is indirectly owned by Williams Partners L.P. (WPZ), a publicly traded Delaware limited partnership, which is consolidated by The Williams Companies, Inc. (Williams). On February 2, 2015, WPZ was merged into Access Midstream Partners, L.P. (ACMP), another publicly traded limited partnership consolidated by Williams. ACMP was the surviving partnership and was subsequently renamed WPZ. At March 31, 2016, Williams holds an approximate 60 percent interest in WPZ, comprised of an approximate 58 percent limited partner interest and all of the 2 percent general partner interest.

On September 28, 2015, Williams publicly announced in a press release that it had entered into an Agreement and Plan of Merger (Merger Agreement) with Energy Transfer Equity, L.P. (Energy Transfer) and certain of its affiliates. The Merger Agreement provides that, subject to the satisfaction of customary closing conditions, Williams will be merged with and into the newly formed Energy Transfer Corp LP (ETC) (ETC Merger) with ETC surviving the ETC Merger. Energy Transfer formed ETC as a limited partnership that will be treated as a corporation for U.S. federal income tax purposes. Immediately following the completion of the ETC Merger, ETC will contribute to Energy Transfer all of the assets and liabilities of Williams in exchange for the issuance by Energy Transfer to ETC of a number of Energy Transfer Class E common units equal to the number of ETC common shares issued to Williams stockholders in the ETC Merger. WPZ expects to retain its current name and remain a publicly traded limited partnership following the ETC Merger.

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

General

The accompanying interim financial statements do not include all the notes in our annual financial statements, and therefore, should be read in conjunction with the financial statements and notes thereto in our 2015 Annual Report on Form 10-K. The accompanying unaudited financial statements include all adjustments both normal recurring and others which, in the opinion of our management, are necessary to present fairly our interim financial statements.

The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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.

Accounting Standards Issued But Not Yet Adopted

In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02 "Leases (Topic 842)" (ASU 2016-02). ASU 2016-02 establishes a comprehensive new lease accounting model. The new standard clarifies the definition of a lease, requires a dual approach to lease classification similar to current lease classifications, and causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset. The new standard is effective for interim and annual periods beginning after December 15, 2018. Early adoption is permitted. The new standard requires a modified retrospective transition for capital or operating leases existing at or entered into after the beginning of the earliest comparative period presented in the financial statements. We are evaluating the impact of the new standards on our financial statements.

In May 2014, the FASB issued ASU 2014-09 establishing Accounting Standards Codification Topic 606, "Revenue from Contracts with Customers" (ASC 606). ASC 606 establishes a comprehensive new revenue recognition model designed to depict the transfer of goods or services to a customer in an amount that reflects the consideration the entity expects to be entitled to receive in exchange for those goods or services and requires significantly enhanced revenue disclosures. In April 2016, the FASB issued ASU 2016-10 "Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing" (ASU 2016-10) to clarify aspects of Topic 606 related to identifying performance obligations and licensing implementation guidance. In August 2015, the FASB issued ASU 2015-14 "Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date" (ASU 2015-14). Per ASU 2015-14, the standard is effective for interim and annual reporting periods beginning after December 15, 2017. ASC 606 allows either full retrospective or modified retrospective transition and early adoption is permitted for annual periods beginning after December 15, 2016. We continue to evaluate both the impact of this new standard on our financial statements and the transition method we will utilize for adoption.