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Debt - Additional Information (Detail) - USD ($)
1 Months Ended 6 Months Ended
Feb. 28, 2018
Jan. 31, 2018
Jun. 30, 2018
Jun. 07, 2018
Mar. 31, 2018
Feb. 01, 2018
Dec. 31, 2017
Debt Instrument [Line Items]              
Total borrowings at face value     $ 17,631,000,000       $ 17,032,000,000
APC RCF [Member]              
Debt Instrument [Line Items]              
Line of credit, maximum capacity   $ 3,000,000,000          
Line of credit, expiration date   Jan. 23, 2022          
Line of credit, outstanding borrowings     $ 0        
364-Day Credit Facility Due 2017 [Member]              
Debt Instrument [Line Items]              
Line of credit, maximum capacity   $ 2,000,000,000          
Line of credit, expiration date   Jan. 12, 2019          
Debt instrument, term     364 days        
Line of credit, outstanding borrowings     $ 0        
WES RCF [Member]              
Debt Instrument [Line Items]              
Borrowings, credit facility     260,000,000        
Repayments, credit facility     (630,000,000)        
Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member]              
Debt Instrument [Line Items]              
Estimated fair value of total borrowings     17,500,000,000       17,700,000,000
TEUs - senior amortizing notes due 2018 [Member]              
Debt Instrument [Line Items]              
Debt instrument, stated interest rate       1.50%      
8.70% Senior Notes due March 2019              
Debt Instrument [Line Items]              
Outstanding borrowings     $ 600,000,000        
Line of credit, interest rate     8.70%        
6.950% Senior Notes Due June 2019 [Member]              
Debt Instrument [Line Items]              
Outstanding borrowings     $ 300,000,000        
Line of credit, interest rate     6.95%        
Zero-Coupon Senior Notes [Member]              
Debt Instrument [Line Items]              
Debt Instrument, earliest call date     Oct. 10, 2018        
Zero-Coupon Senior Notes [Member] | Accreted Value at Next Potential Put Date [Member]              
Debt Instrument [Line Items]              
Debt instrument, accreted value     $ 930,000,000        
WES 4.500% Senior Notes due 2028 [Member]              
Debt Instrument [Line Items]              
Borrowings during period     394,000,000        
WES 5.300% Senior Notes due 2048 [Member]              
Debt Instrument [Line Items]              
Borrowings during period     687,000,000        
Western Gas Partners, LP [Member]              
Debt Instrument [Line Items]              
Total borrowings at face value     4,220,000,000       3,490,000,000
Western Gas Partners, LP [Member] | WES RCF [Member]              
Debt Instrument [Line Items]              
Line of credit, maximum capacity $ 1,500,000,000            
Line of credit, expiration date Feb. 26, 2023 Feb. 26, 2020          
Line of credit, outstanding borrowings     0        
Line of credit, expandable maximum capacity $ 2,000,000,000            
Borrowings, credit facility     260,000,000        
Repayments, credit facility     (630,000,000)        
Letters of credit, outstanding     5,000,000        
Line of credit, available borrowing capacity     $ 1,495,000,000        
Western Gas Partners, LP [Member] | 7.050% Debentures due 2018 [Member]              
Debt Instrument [Line Items]              
Debt instrument, stated interest rate     7.05%        
Western Gas Partners, LP [Member] | WES Senior Notes due August 2018 [Member]              
Debt Instrument [Line Items]              
Debt instrument, stated interest rate     2.60%        
Total borrowings at face value     $ 350,000,000        
Western Gas Partners, LP [Member] | WES 4.500% Senior Notes due 2028 [Member]              
Debt Instrument [Line Items]              
Debt instrument, stated interest rate     4.50%   4.50%    
Total borrowings at face value         $ 400,000,000    
Borrowings during period     $ 394,000,000        
Western Gas Partners, LP [Member] | WES 5.300% Senior Notes due 2048 [Member]              
Debt Instrument [Line Items]              
Debt instrument, stated interest rate     5.30%   5.30%    
Total borrowings at face value         $ 700,000,000    
Borrowings during period     $ 687,000,000        
Western Gas Equity Partners, LP excluding WES [Member]              
Debt Instrument [Line Items]              
Total borrowings at face value [1]     28,000,000       $ 28,000,000
Western Gas Equity Partners, LP excluding WES [Member] | WGP RCF [Member]              
Debt Instrument [Line Items]              
Line of credit, expiration date Mar. 14, 2019            
Line of credit, outstanding borrowings     28,000,000        
Line of credit, available borrowing capacity   $ 250,000,000 $ 7,000,000     $ 35,000,000  
Line of credit, interest rate     4.10%        
[1] Excludes WES.