Debt and Interest Expense - Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
Carrying value, beginning balance	$ 13,557us-gaap_LongTermDebt	$ 13,269us-gaap_LongTermDebt
Debt Instrument [Line Items]
Other, net	39	38
Carrying value, ending balance	15,071us-gaap_LongTermDebt	13,557us-gaap_LongTermDebt
WES 2.600% Senior Notes due 2018 [Member] \| Western Gas Partners, LP [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Issuance	101	250
Debt instrument, stated interest rate	2.60%	2.60%
Debt instrument, maturity date	Aug. 15, 2018	Aug. 15, 2018
WES RCF [Member] \| Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings	1,160	710
Repayments of credit facilities	(650)	(710)
WES 5.450% Senior Notes due 2044 [Member] \| Western Gas Partners, LP [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Issuance	394
Debt instrument, stated interest rate	5.45%
Debt instrument, maturity date	Apr. 01, 2044
3.450% Senior Notes due 2024 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Issuance	624
Debt instrument, stated interest rate	3.45%
Debt instrument, maturity date	Jul. 15, 2024
4.500% Senior Notes due 2044 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Issuance	621
Debt instrument, stated interest rate	4.50%
Debt instrument, maturity date	Jul. 15, 2044
7.625% Senior Notes due 2014 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Repayments of debt	(500)
Debt instrument, stated interest rate	7.625%
Debt instrument, maturity date	Mar. 15, 2014
5.750% Senior Notes due 2014 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Repayments of debt	$ (275)
Debt instrument, stated interest rate	5.75%
Debt instrument, maturity date	Jun. 15, 2014

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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