Basis of Presentation (Notes)	6 Months Ended
Jun. 30, 2015
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 Williams Partners L.P. At June 30, 2015, Williams holds an approximate 60 percent interest in WPZ, comprised of an approximate 58 percent limited partner interest and all of WPZ’s 2 percent general partner interest. 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 2014 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. A reclassification within the investing activities of the Statement of Cash Flows, between Capital expenditures, net of equity AFUDC* and Contributions and advances for construction costs of $0.8 million for the six months ended June 30, 2014, has been made to correct the 2014 financial statements to conform to the 2015 presentation. Accounting Standards Issued But Not Yet Adopted In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-11 "Simplifying the Measurement of Inventory" (ASU 2015-11). ASU 2015-11 simplifies the guidance on the subsequent measurement of inventory, excluding inventory measured using last in, first out or the retail inventory method. Under the new standard, in scope inventory should be measured at the lower of cost and net realizable value. The new standard is effective for interim and annual periods beginning after December 15, 2016, with early adoption permitted. We are evaluating the impact of the new standard. In April 2015, the FASB issued ASU 2015-03 "Interest - Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs" (ASU 2015-03). ASU 2015-03 simplifies the presentation of debt issuance costs by requiring such costs be presented as a deduction from the corresponding debt liability. The guidance is effective for financial statements issued for reporting periods beginning after December 15, 2015, and interim periods within the reporting periods and requires retrospective presentation. We are evaluating the impact of the new standard. In February 2015, the FASB issued ASU 2015-02 "Amendments to the Consolidation Analysis" (ASU 2015-02). ASU 2015-02 alters the models used to determine consolidation conclusions for certain entities, including limited partnerships, and may require additional disclosures. The ASU is effective for financial statements issued for reporting periods beginning after December 15, 2015, and interim periods within the reporting periods with either retrospective or modified retrospective presentation allowed. We are currently evaluating the impact of the new standard 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. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within the reporting period. 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 Williams Partners L.P. At June 30, 2015, Williams holds an approximate 60 percent interest in WPZ, comprised of an approximate 58 percent limited partner interest and all of WPZ’s 2 percent general partner interest.

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 2014 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.

A reclassification within the investing activities of the Statement of Cash Flows, between Capital expenditures, net of equity AFUDC* and Contributions and advances for construction costs of $0.8 million for the six months ended June 30, 2014, has been made to correct the 2014 financial statements to conform to the 2015 presentation.

Accounting Standards Issued But Not Yet Adopted

In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-11 "Simplifying the Measurement of Inventory" (ASU 2015-11). ASU 2015-11 simplifies the guidance on the subsequent measurement of inventory, excluding inventory measured using last in, first out or the retail inventory method. Under the new standard, in scope inventory should be measured at the lower of cost and net realizable value. The new standard is effective for interim and annual periods beginning after December 15, 2016, with early adoption permitted. We are evaluating the impact of the new standard.

In April 2015, the FASB issued ASU 2015-03 "Interest - Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs" (ASU 2015-03). ASU 2015-03 simplifies the presentation of debt issuance costs by requiring such costs be presented as a deduction from the corresponding debt liability. The guidance is effective for financial statements issued for reporting periods beginning after December 15, 2015, and interim periods within the reporting periods and requires retrospective presentation. We are evaluating the impact of the new standard.

In February 2015, the FASB issued ASU 2015-02 "Amendments to the Consolidation Analysis" (ASU 2015-02). ASU 2015-02 alters the models used to determine consolidation conclusions for certain entities, including limited partnerships, and may require additional disclosures. The ASU is effective for financial statements issued for reporting periods beginning after December 15, 2015, and interim periods within the reporting periods with either retrospective or modified retrospective presentation allowed. We are currently evaluating the impact of the new standard 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. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within the reporting period. 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.