Debt and Interest Expense - Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Debt Disclosure [Abstract]
Carrying value, beginning balance	$ 15,230	$ 12,787
Debt Instrument [Line Items]
Other, net	35	33
Carrying value, ending balance	13,269	15,230
Senior Notes, 5 Point 375 Percent, Due 2021 [Member] \| Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.375%
Debt instrument, maturity date	Jun. 01, 2021
Senior Notes, 5 Point 375 Percent, Due 2021 [Member] \| Western Gas Partners Limited Partnership [Member] \| Issuance Of Debt [Member]
Debt Instrument [Line Items]
Issuances and Borrowings		494
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Repayments	(2,500)
Revolving Credit Facility [Member] \| Borrowings [Member]
Debt Instrument [Line Items]
Issuances and Borrowings		2,500
Revolving Credit Facility [Member] \| Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Repayments	(374)
Revolving Credit Facility [Member] \| Western Gas Partners Limited Partnership [Member] \| Borrowings [Member]
Debt Instrument [Line Items]
Issuances and Borrowings	374	570
Revolving Credit Facility and Term Loan [Member] \| Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Repayments		(869)
Senior Notes, 6 Point 875 Percent, Due 2011 [Member]
Debt Instrument [Line Items]
Repayments		(285)
Debt instrument, stated interest rate		6.875%
Debt instrument, maturity date		Sep. 15, 2011
Senior Notes, 4 Point 000 Percent, Due 2022 [Member] \| Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.00%
Debt instrument, maturity date	Jul. 01, 2022
Senior Notes, 4 Point 000 Percent, Due 2022 [Member] \| Western Gas Partners Limited Partnership [Member] \| Issuance Of Debt [Member]
Debt Instrument [Line Items]
Issuances and Borrowings	674
Senior Notes, 6 Point 125 Percent, Due 2012 [Member]
Debt Instrument [Line Items]
Repayments	(131)
Debt instrument, stated interest rate	6.125%
Debt instrument, maturity date	Mar. 15, 2012
Senior Notes, 5 Point 000 Percent, Due 2012 [Member]
Debt Instrument [Line Items]
Repayments	$ (39)
Debt instrument, stated interest rate	5.00%
Debt instrument, maturity date	Oct. 01, 2012

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.8)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 8

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Section 45

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Decrease for amounts repaid on the debt instrument for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

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-Paragraph 1

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Increase of additional borrowings on existing and new debt instruments.

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- Definition

Interest rate stated in the contractual debt agreement.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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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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