Debt and Interest Expense - Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2013	Mar. 31, 2013
Debt Disclosure [Abstract]
Carrying value, beginning balance	$ 13,663	$ 13,269
Debt Instrument [Line Items]
Other, net	10	9
Carrying value, ending balance	13,538	13,663
Western Gas Partners Limited Partnership [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings	110	385
Repayments	$ (245)

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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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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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity that is collateralized (backed by pledge, mortgage or other lien in the entity's assets).

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- Definition

The cash outflow to pay off an obligation from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity.

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