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Debt and Interest Expense - Outstanding Debt Table (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 17,312 $ 16,687  
Total long-term debt (2) [1] 15,718 15,092  
Net unamortized discounts and premiums (1) [2] (1,581) (1,616)  
Total borrowings 15,731 15,071 $ 13,557
Capital lease obligation 20 21  
Less current portion of long-term debt 33 0  
Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Total long-term debt (2) 2,700 2,400  
Senior Notes [Member] | 5.950% Senior Notes due 2016 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 1,750 1,750  
Debt instrument, stated interest rate 5.95%    
Debt instrument, maturity date Sep. 15, 2016    
Senior Notes [Member] | 6.375% Senior Notes due 2017 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 2,000 2,000  
Debt instrument, stated interest rate 6.375%    
Debt instrument, maturity date Sep. 15, 2017    
Senior Notes [Member] | 7.050% Debentures due 2018 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 114 114  
Debt instrument, stated interest rate 7.05%    
Debt instrument, maturity date May 15, 2018    
Senior Notes [Member] | Tangible Equity Units - senior amortizing notes [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 85 0  
Debt instrument, stated interest rate 1.50%    
Debt instrument, maturity date Jun. 07, 2018    
Senior Notes [Member] | WES 2.600% Senior Notes due 2018 [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 350 $ 350  
Debt instrument, stated interest rate 2.60% 2.60%  
Debt instrument, maturity date Aug. 15, 2018 Aug. 15, 2018  
Senior Notes [Member] | 6.950% Senior Notes due 2019 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 300 $ 300  
Debt instrument, stated interest rate 6.95%    
Debt instrument, maturity date Jun. 15, 2019    
Senior Notes [Member] | 8.700% Senior Notes due 2019 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 600 600  
Debt instrument, stated interest rate 8.70%    
Debt instrument, maturity date Mar. 15, 2019    
Senior Notes [Member] | WES 5.375% Senior Notes due 2021 [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 500 500  
Debt instrument, stated interest rate 5.375%    
Debt instrument, maturity date Jun. 01, 2021    
Senior Notes [Member] | WES 4.000% Senior Notes due 2022 [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 670 670  
Debt instrument, stated interest rate 4.00%    
Debt instrument, maturity date Jun. 01, 2022    
Senior Notes [Member] | 3.450% Senior Notes due 2024 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 625 $ 625  
Debt instrument, stated interest rate 3.45% 3.45%  
Debt instrument, maturity date Jul. 15, 2024 Jul. 15, 2024  
Senior Notes [Member] | 6.950% Senior Notes due 2024 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 650 $ 650  
Debt instrument, stated interest rate 6.95%    
Debt instrument, maturity date Jun. 01, 2024    
Senior Notes [Member] | WES 3.950% Senior Notes due 2025 | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 500 0  
Debt instrument, stated interest rate 3.95%    
Debt instrument, maturity date May 15, 2025    
Senior Notes [Member] | 7.500% Debentures due 2026 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 112 112  
Debt instrument, stated interest rate 7.50%    
Debt instrument, maturity date Oct. 15, 2026    
Senior Notes [Member] | 7.000% Debentures due 2027 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 54 54  
Debt instrument, stated interest rate 7.00%    
Debt instrument, maturity date Nov. 15, 2027    
Senior Notes [Member] | 7.125% Debentures due 2027 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 150 150  
Debt instrument, stated interest rate 7.125%    
Debt instrument, maturity date Oct. 15, 2027    
Senior Notes [Member] | 6.625% Debentures due 2028 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 17 17  
Debt instrument, stated interest rate 6.625%    
Debt instrument, maturity date Jan. 15, 2028    
Senior Notes [Member] | 7.150% Debentures due 2028 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 235 235  
Debt instrument, stated interest rate 7.15%    
Debt instrument, maturity date May 15, 2028    
Senior Notes [Member] | 7.200% Debentures due 2029 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 135 135  
Debt instrument, stated interest rate 7.20%    
Debt instrument, maturity date Mar. 15, 2029    
Senior Notes [Member] | 7.950% Debentures due 2029 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 117 117  
Debt instrument, stated interest rate 7.95%    
Debt instrument, maturity date Apr. 15, 2029    
Senior Notes [Member] | 7.500% Senior Notes due 2031 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 900 900  
Debt instrument, stated interest rate 7.50%    
Debt instrument, maturity date May 01, 2031    
Senior Notes [Member] | 7.875% Senior Notes due 2031 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 500 500  
Debt instrument, stated interest rate 7.875%    
Debt instrument, maturity date Sep. 15, 2031    
Senior Notes [Member] | Zero-Coupon Senior Notes due 2036 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 2,360 2,360  
Debt instrument, maturity date Oct. 10, 2036    
Senior Notes [Member] | 6.450% Senior Notes due 2036 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 1,750 1,750  
Debt instrument, stated interest rate 6.45%    
Debt instrument, maturity date Sep. 15, 2036    
Senior Notes [Member] | 7.950% Senior Notes due 2039 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 325 325  
Debt instrument, stated interest rate 7.95%    
Debt instrument, maturity date Jun. 15, 2039    
Senior Notes [Member] | 6.200% Senior Notes due 2040 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 750 750  
Debt instrument, stated interest rate 6.20%    
Debt instrument, maturity date Mar. 15, 2040    
Senior Notes [Member] | 4.500% Senior Notes due 2044 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 625 $ 625  
Debt instrument, stated interest rate 4.50% 4.50%  
Debt instrument, maturity date Jul. 15, 2044 Jul. 15, 2044  
Senior Notes [Member] | WES 5.450% Senior Notes due 2044 [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 400 $ 400  
Debt instrument, stated interest rate 5.45% 5.45%  
Debt instrument, maturity date Apr. 01, 2044 Apr. 01, 2044  
Senior Notes [Member] | 7.730% Debentures due 2096 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 61 $ 61  
Debt instrument, stated interest rate 7.73%    
Debt instrument, maturity date Sep. 15, 2096    
Senior Notes [Member] | 7.500% Debentures due 2096 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 78 78  
Debt instrument, stated interest rate 7.50%    
Debt instrument, maturity date Nov. 01, 2096    
Senior Notes [Member] | 7.250% Debentures due 2096 [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 49 49  
Debt instrument, stated interest rate 7.25%    
Debt instrument, maturity date Nov. 15, 2096    
Commercial Paper [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 250 0  
Revolving Credit Facility [Member] | WES RCF [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 300 $ 510  
[1] The total long-term debt balance for WES was $2.7 billion at December 31, 2015, and $2.4 billion at December 31, 2014.
[2] Unamortized discounts and premiums are amortized over the term of the related debt.