Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business combinations policy	Presentation of WES assets. References to “WES assets” refer collectively to the assets indirectly owned by WGP, through its partnership interests in WES, as of September 30, 2013. Because Anadarko controls WES through its ownership and control of WGP, which owns WES GP, each of WES’s acquisitions of assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, WES assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by WES. Further, after an acquisition of assets from Anadarko, WES and WGP (by virtue of its consolidation of WES) may be required to recast their financial statements to include the activities of such assets as of the date of common control. See Note 2. For those periods requiring recast, the consolidated financial statements for periods prior to the acquisition of WES assets from Anadarko, including the Non-Operated Marcellus Interest, have been prepared from Anadarko’s historical cost-basis accounts and may not necessarily be indicative of the actual results of operations that would have occurred if WES had owned the assets during the periods reported. Net income attributable to WES assets for periods prior to WES’s acquisition of such assets is not allocated to the limited partners for purposes of calculating net income per common unit. Anadarko-Operated Marcellus Interest acquisition. The Anadarko-Operated Marcellus Interest acquisition has been accounted for under the acquisition method of accounting. The assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition were recorded in the consolidated balance sheet at their estimated fair values as of the acquisition date. Results of operations attributable to the Anadarko-Operated Marcellus Interest were included in the consolidated statements of income beginning on the acquisition date in the first quarter of 2013.
Net income per common unit policy	Net income per common unit. Net income attributable to periods prior to WGP’s IPO is attributable to subsidiaries of Anadarko and therefore not allocated to the limited partners for purposes of calculating net income per common unit. As a result, pre-IPO net income, representing the financial results prior to WGP’s IPO on December 12, 2012, has been excluded from the limited partners’ interest in net income.
Fair value policy	Note receivable from and amounts payable to Anadarko. Concurrently with the closing of WES’s May 2008 IPO, WES loaned $260.0 million to Anadarko in exchange for a 30-year note bearing interest at a fixed annual rate of 6.50%, payable quarterly. The fair value of the note receivable from Anadarko was approximately $301.5 million and $334.8 million at September 30, 2013, and December 31, 2012, respectively. The fair value of the note reflects consideration of credit risk and any premium or discount for the differential between the stated interest rate and quarter-end market interest rate, based on quoted market prices of similar debt instruments. Accordingly, the fair value of the note receivable from Anadarko is measured using Level 2 inputs.
Capitalized interest policy	Mont Belvieu JV acquisition. The acquisition purchase price represented WES’s 25% share of construction costs incurred by the joint venture partner and 25% of the capitalized interest charged to the financial statements of the Mont Belvieu JV up to the date of acquisition. The allocated capitalized interest is reflected as a component of the equity investment balance recorded upon acquisition. Based on the total estimated net project cost, the construction of the fractionation facilities owned by the Mont Belvieu JV is considered a significant project and satisfies criteria for capitalization of interest. Capitalization of interest subsequent to the acquisition is treated as a basis difference between the cost of the investment and the underlying equity in the net assets of the Mont Belvieu JV. WES will begin to amortize the capitalized interest recognized subsequent to the acquisition upon completion of the facilities, and will reflect the amortization as an adjustment to equity earnings from the Mont Belvieu JV.

Disclosure of accounting policy for completed business combinations (purchase method, acquisition method or combination of entities under common control). This accounting policy may include a general discussion of the purchase method or acquisition method of accounting (including for example, the treatment accorded contingent consideration, the identification of assets and liabilities, the purchase price allocation process, how the fair values of acquired assets and liabilities are determined) and the entity's specific application thereof. An entity that acquires another entity in a leveraged buyout transaction generally discloses the accounting policy followed by the acquiring entity in determining the basis used to value its interest in the acquired entity, and the rationale for that accounting policy.

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- Definition

Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements.

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