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Debt and Interest Expense - Debt Activity Table (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Debt Disclosure [Abstract]    
Carrying value, beginning balance $ 15,071 $ 13,557
Debt Instrument [Line Items]    
Other, net 41 39
Carrying value, ending balance 15,731 15,071
Commercial Paper [Member]    
Debt Instrument [Line Items]    
Borrowings, commercial paper 250 [1]  
Commercial Paper [Member] | Maturities Greater Than 90 Days [Member]    
Debt Instrument [Line Items]    
Repayments, commercial paper (106)  
WES RCF [Member] | Western Gas Partners, LP [Member] | Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Borrowings, credit facilities 400 1,160
Repayments of credit facilities (610) (650)
5.0 billion Facility [Member] | Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Borrowings, credit facilities 1,500  
Repayments of credit facilities (1,500)  
364-Day Facility due 2016 [Member] | Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Borrowings, credit facilities 1,800  
Repayments of credit facilities $ (1,800)  
Senior Notes [Member] | WES 2.600% Senior Notes due 2018 [Member] | Western Gas Partners, LP [Member]    
Debt Instrument [Line Items]    
Issuance   $ 101
Debt instrument, stated interest rate 2.60% 2.60%
Debt instrument, maturity date Aug. 15, 2018 Aug. 15, 2018
Senior Notes [Member] | WES 5.450% Senior Notes due 2044 [Member] | Western Gas Partners, LP [Member]    
Debt Instrument [Line Items]    
Issuance   $ 394
Debt instrument, stated interest rate 5.45% 5.45%
Debt instrument, maturity date Apr. 01, 2044 Apr. 01, 2044
Senior Notes [Member] | 3.450% Senior Notes due 2024 [Member]    
Debt Instrument [Line Items]    
Issuance   $ 624
Debt instrument, stated interest rate 3.45% 3.45%
Debt instrument, maturity date Jul. 15, 2024 Jul. 15, 2024
Senior Notes [Member] | 4.500% Senior Notes due 2044 [Member]    
Debt Instrument [Line Items]    
Issuance   $ 621
Debt instrument, stated interest rate 4.50% 4.50%
Debt instrument, maturity date Jul. 15, 2044 Jul. 15, 2044
Senior Notes [Member] | 7.625% Senior Notes due 2014 [Member]    
Debt Instrument [Line Items]    
Repayments of debt   $ (500)
Debt instrument, stated interest rate   7.625%
Debt instrument, maturity date   Mar. 15, 2014
Senior Notes [Member] | 5.750% Senior Notes due 2014 [Member]    
Debt Instrument [Line Items]    
Repayments of debt   $ (275)
Debt instrument, stated interest rate   5.75%
Debt instrument, maturity date   Jun. 15, 2014
Senior Notes [Member] | WES 3.950% Senior Notes due 2025 | Western Gas Partners, LP [Member]    
Debt Instrument [Line Items]    
Issuance $ 494  
Debt instrument, stated interest rate 3.95%  
Debt instrument, maturity date May 15, 2025  
Senior Notes [Member] | Tangible Equity Units - senior amortizing notes [Member]    
Debt Instrument [Line Items]    
Issuance $ 101  
Repayments of debt $ (16)  
Debt instrument, stated interest rate 1.50%  
Debt instrument, maturity date Jun. 07, 2018  
[1] Includes repayments of $(106) million related to commercial paper notes with maturities greater than 90 days.