Debt and Interest Expense - Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Debt Disclosure [Abstract]
Carrying value, beginning balance	$ 15,071
Debt Instrument [Line Items]
Other, net	10
Carrying value, ending balance	16,844
Commercial Paper [Member]
Debt Instrument [Line Items]
Borrowings, commercial paper	1,153
$5.0 billion Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings, credit facility	1,500
Repayments, credit facility	(1,500)
364-Day Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings, credit facility	1,800
Repayments, credit facility	(1,300)
WES RCF [Member] \| Revolving Credit Facility [Member] \| Western Gas Partners, LP [Member]
Debt Instrument [Line Items]
Borrowings, credit facility	140
Repayments, credit facility	$ (30)

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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The cash inflow from borrowing by issuing commercial paper.

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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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