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Debt and Interest Expense - Debt Activity Table (Detail)
$ in Millions
6 Months Ended
Jun. 30, 2015
USD ($)
Debt Disclosure [Abstract]  
Balance at December 31, 2014 $ 15,071
Debt Instrument [Line Items]  
Other, net 19
Balance at June 30, 2015 16,037
Commercial Paper [Member]  
Debt Instrument [Line Items]  
Borrowings, commercial paper [1] 592
Commercial Paper [Member] | Maturities Greater Than 90 Days [Member]  
Debt Instrument [Line Items]  
Repayments, commercial paper (37)
7.50% Tangible Equity Units [Member]  
Debt Instrument [Line Items]  
Issuance 101
$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 (1,800)
WES RCF [Member] | Revolving Credit Facility [Member] | Western Gas Partners, LP [Member]  
Debt Instrument [Line Items]  
Borrowings, credit facility 280
Repayments, credit facility (520)
Senior Notes [Member] | WES 3.950% Senior Notes Due 2025 [Member] | Western Gas Partners, LP [Member]  
Debt Instrument [Line Items]  
Issuance $ 494
[1] Includes repayments of $37 million related to commercial paper notes with maturities greater than 90 days.