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Debt and Interest Expense - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 11 Months Ended 12 Months Ended
Feb. 16, 2018
Jan. 31, 2018
Jun. 30, 2016
Nov. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2006
Feb. 01, 2018
Oct. 31, 2016
Mar. 31, 2016
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 17,032,000,000 $ 16,706,000,000          
Losses on early retirement and redemption of debt         2,000,000 155,000,000 $ 0        
Premiums paid for early retirement and redemption of debt           144,000,000          
FPSO capital lease obligation         231,000,000 245,000,000          
Accumulated depreciation of capital lease assets         45,000,000 10,000,000          
Five-Year Credit Facility [Member]                      
Debt Instrument [Line Items]                      
Line of credit, maximum capacity         3,000,000,000            
Line of credit, outstanding borrowings         $ 0            
Five-Year Credit Facility [Member] | Minimum [Member] | Euro Interbank Offered Rate or Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         0.00%            
Five-Year Credit Facility [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Ratio of indebtedness to total capital         0.65            
Five-Year Credit Facility [Member] | Maximum [Member] | Euro Interbank Offered Rate or Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.65%            
364-Day Facility [Member]                      
Debt Instrument [Line Items]                      
Line of credit, maximum capacity         $ 2,000,000,000            
Debt instrument, term         364 days            
Line of credit, outstanding borrowings         $ 0            
364-Day Facility [Member] | Minimum [Member] | London Interbank Offered Rate or Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         0.00%            
364-Day Facility [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Ratio of indebtedness to total capital         0.65            
364-Day Facility [Member] | Maximum [Member] | London Interbank Offered Rate or Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.675%            
Commercial Paper [Member]                      
Debt Instrument [Line Items]                      
Line of credit, maximum capacity         $ 3,000,000,000            
Commercial paper, outstanding borrowings         $ 0            
Commercial Paper [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, term         397 days            
WES RCF [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 370,000,000 28,000,000          
WGP RCF [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 28,000,000            
WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Line of credit, variable rate floor         0.00%            
WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.00%            
WGP RCF [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         0.50%            
WGP RCF [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         2.00%            
WGP RCF [Member] | Minimum [Member] | Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.00%            
WGP RCF [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         2.75%            
WGP RCF [Member] | Maximum [Member] | Base Rate [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.75%            
Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member]                      
Debt Instrument [Line Items]                      
Estimated fair value of total borrowings         $ 17,700,000,000 $ 17,100,000,000          
March 2016 Senior Notes Issuances [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount                     $ 3,000,000,000
Portion of 6.375% Senior Notes due 2017 [Member]                      
Debt Instrument [Line Items]                      
Amount of debt retired and redeemed     $ 1,250,000,000                
6.375% Senior Notes due 2017 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount     $ 2,000,000,000                
Debt instrument, stated interest rate     6.375%     6.375%          
Debt instrument, maturity date     Sep. 15, 2017     Sep. 15, 2017          
5.950% Senior Notes due 2016 [Member]                      
Debt Instrument [Line Items]                      
Amount of debt retired and redeemed     $ 1,750,000,000                
Debt instrument, stated interest rate     5.95%     5.95%          
Debt instrument, maturity date     Sep. 15, 2016     Sep. 15, 2016          
Remaining Portion of 6.375% Senior Notes due 2017 [Member]                      
Debt Instrument [Line Items]                      
Amount of debt retired and redeemed           $ 750,000,000          
Zero Coupon Senior Notes due 2036 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 2,360,000,000 2,360,000,000          
Debt instrument, maturity date         Oct. 10, 2036            
Loan proceeds upon issuing debt               $ 500,000,000      
Yield to maturity         5.24%            
Debt instrument, accreted value         $ 894,000,000            
WES 4.650% Senior Notes due 2026 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 500,000,000 500,000,000          
Debt instrument, stated interest rate         4.65%            
Debt instrument, maturity date         Jul. 01, 2026            
WES 5.450% Senior Notes due 2044 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 600,000,000 600,000,000          
Debt instrument, stated interest rate         5.45%            
Debt instrument, maturity date         Apr. 01, 2044            
WES 2.600% Senior Notes due 2018 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 350,000,000 350,000,000          
Debt instrument, stated interest rate         2.60%            
Debt instrument, maturity date         Aug. 15, 2018            
FPSO Capital Lease [Member]                      
Debt Instrument [Line Items]                      
Anadarko's nonoperated interest         19.00%            
FPSO capital lease obligation         $ 225,000,000            
FPSO capital lease asset         $ 225,000,000            
FPSO capital lease initial term         10 years            
FPSO capital lease additional term         10 years            
Capital lease payments made         $ 44,000,000            
Western Gas Partners, LP [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         3,490,000,000 3,120,000,000          
FPSO capital lease obligation         0 $ 0          
Western Gas Partners, LP [Member] | WES RCF [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         370,000,000            
Line of credit, maximum capacity         1,200,000,000            
Line of credit, expiration date       Feb. 26, 2019   Feb. 26, 2020          
Line of credit, outstanding borrowings         370,000,000            
Line of credit, available borrowing capacity         825,000,000            
Outstanding letters of credit         $ 5,000,000            
Line of credit, interest rate         2.87%            
Western Gas Partners, LP [Member] | WES RCF [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         0.975%            
Western Gas Partners, LP [Member] | WES RCF [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Applicable margin added         1.45%            
Western Gas Partners, LP [Member] | WES 4.650% Senior Notes due 2026 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 500,000,000 $ 500,000,000          
Debt instrument, stated interest rate         4.65%            
Debt instrument, maturity date         Jul. 12, 2026            
Western Gas Partners, LP [Member] | WES 5.450% Senior Notes due 2044 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 600,000,000 600,000,000       $ 200,000,000  
Debt instrument, stated interest rate         5.45%            
Debt instrument, maturity date         Apr. 01, 2044            
Western Gas Partners, LP [Member] | WES 2.600% Senior Notes due 2018 [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount         $ 350,000,000 350,000,000          
Debt instrument, stated interest rate         2.60%            
Western Gas Equity Partners, LP excluding WES [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount [1]         $ 28,000,000 28,000,000          
FPSO capital lease obligation [1]         0 0          
Western Gas Equity Partners, LP excluding WES [Member] | WES RCF [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount [1]           $ 28,000,000          
Western Gas Equity Partners, LP excluding WES [Member] | WGP RCF [Member]                      
Debt Instrument [Line Items]                      
Debt instrument, principal amount [1]         28,000,000            
Line of credit, maximum capacity         250,000,000            
Line of credit, expandable maximum capacity         $ 500,000,000            
Line of credit, expiration date         Mar. 14, 2019            
Line of credit, outstanding borrowings         $ 28,000,000            
Line of credit, available borrowing capacity         $ 222,000,000            
Line of credit, interest rate         3.57%            
Subsequent Event [Member] | Five-Year Credit Facility [Member]                      
Debt Instrument [Line Items]                      
Line of credit, expiration date   Jan. 23, 2022                  
Subsequent Event [Member] | 364-Day Facility [Member]                      
Debt Instrument [Line Items]                      
Line of credit, expiration date   Jan. 12, 2019                  
Subsequent Event [Member] | Western Gas Partners, LP [Member] | WES RCF [Member]                      
Debt Instrument [Line Items]                      
Line of credit, expandable maximum capacity $ 1,500,000,000                    
Line of credit, expiration date Feb. 26, 2023                    
Subsequent Event [Member] | Western Gas Equity Partners, LP excluding WES [Member] | WGP RCF [Member]                      
Debt Instrument [Line Items]                      
Line of credit, available borrowing capacity                 $ 35,000,000    
[1] Excludes WES.