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Debt and Interest Expense - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Jan. 19, 2016
Dec. 31, 2015
Dec. 31, 2015
Dec. 31, 2006
Jan. 23, 2015
Dec. 31, 2014
Feb. 25, 2014
Debt Instrument [Line Items]              
Debt instrument, principal amount   $ 17,312,000,000 $ 17,312,000,000     $ 16,687,000,000  
Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member]              
Debt Instrument [Line Items]              
Estimated fair value of total borrowings   15,700,000,000 $ 15,700,000,000     17,400,000,000  
Senior Notes [Member] | Zero-Coupon Senior Notes due 2036 [Member]              
Debt Instrument [Line Items]              
Loan proceeds upon issuing debt       $ 500,000,000      
Debt instrument, maturity date     Oct. 10, 2036        
Debt instrument, principal amount   $ 2,360,000,000 $ 2,360,000,000     2,360,000,000  
Yield to maturity   5.24% 5.24%        
Debt instrument, accreted value   $ 806,000,000 $ 806,000,000        
Senior Notes [Member] | 5.950% Senior Notes due 2016 [Member]              
Debt Instrument [Line Items]              
Debt instrument, maturity date     Sep. 15, 2016        
Debt instrument, principal amount   $ 1,750,000,000 $ 1,750,000,000     1,750,000,000  
Debt instrument, stated interest rate   5.95% 5.95%        
Amount of current debt outstanding classified as long-term debt on the Company's Consolidated Balance Sheet     $ 1,750,000,000        
Commercial Paper [Member]              
Debt Instrument [Line Items]              
Debt instrument, principal amount   $ 250,000,000 250,000,000     0  
Amount of current debt outstanding classified as long-term debt on the Company's Consolidated Balance Sheet     250,000,000        
Line of credit, maximum capacity   3,000,000,000 3,000,000,000        
Commercial paper, outstanding borrowings   $ 250,000,000 $ 250,000,000        
Commercial paper, weighted-average interest rate   0.98% 0.98%        
Commercial Paper [Member] | Maximum [Member]              
Debt Instrument [Line Items]              
Debt instrument, term     397 days        
Revolving Credit Facility [Member] | Five-Year Facility [Member]              
Debt Instrument [Line Items]              
Debt instrument, maturity date   Jan. 23, 2021          
Line of credit, maximum capacity   $ 3,000,000,000 $ 3,000,000,000        
Debt instrument, term     5 years        
Line of credit, outstanding borrowings   $ 0 $ 0        
Revolving Credit Facility [Member] | Five-Year Facility [Member] | Minimum [Member] | Euro Interbank Offered Rate or Alternate Base Rate [Member]              
Debt Instrument [Line Items]              
Applicable margin added     0.00%        
Revolving Credit Facility [Member] | Five-Year Facility [Member] | Maximum [Member]              
Debt Instrument [Line Items]              
Ratio of indebtedness to total capital   0.65 0.65        
Revolving Credit Facility [Member] | Five-Year Facility [Member] | Maximum [Member] | Euro Interbank Offered Rate or Alternate Base Rate [Member]              
Debt Instrument [Line Items]              
Applicable margin added     1.65%        
Revolving Credit Facility [Member] | 364-Day Facility due 2016 [Member]              
Debt Instrument [Line Items]              
Line of credit, maximum capacity   $ 2,000,000,000 $ 2,000,000,000        
Debt instrument, term     364 days        
Line of credit, outstanding borrowings   $ 0 $ 0        
Revolving Credit Facility [Member] | 364-Day Facility due 2016 [Member] | Minimum [Member] | London Interbank Offered Rate or Alternate Base Rate [Member]              
Debt Instrument [Line Items]              
Applicable margin added     0.00%        
Revolving Credit Facility [Member] | 364-Day Facility due 2016 [Member] | Maximum [Member]              
Debt Instrument [Line Items]              
Ratio of indebtedness to total capital   0.65 0.65        
Revolving Credit Facility [Member] | 364-Day Facility due 2016 [Member] | Maximum [Member] | London Interbank Offered Rate or Alternate Base Rate [Member]              
Debt Instrument [Line Items]              
Applicable margin added     1.675%        
Revolving Credit Facility [Member] | 5.0 billion Facility [Member]              
Debt Instrument [Line Items]              
Line of credit, maximum capacity         $ 5,000,000,000    
Revolving Credit Facility [Member] | 364-Day Facility due 2017 [Member] | Subsequent Event [Member]              
Debt Instrument [Line Items]              
Debt instrument, maturity date Jan. 18, 2017            
Line of credit, maximum capacity $ 2,000,000,000            
Debt instrument, term 364 days            
Revolving Credit Facility [Member] | WES RCF [Member] | Western Gas Partners, LP [Member]              
Debt Instrument [Line Items]              
Debt instrument, principal amount   $ 300,000,000 $ 300,000,000     $ 510,000,000  
Line of credit, maximum capacity   1,200,000,000 1,200,000,000       $ 800,000,000
Line of credit, expandable maximum capacity   1,500,000,000 $ 1,500,000,000        
Line of credit, expiration date     Feb. 26, 2019        
Line of credit, outstanding borrowings   $ 300,000,000 $ 300,000,000        
Line of credit, interest rate   1.73% 1.73%        
Line of credit, available borrowing capacity   $ 894,000,000 $ 894,000,000        
Outstanding letters of credit   $ 6,000,000 $ 6,000,000        
Revolving Credit Facility [Member] | WES RCF [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Western Gas Partners, LP [Member]              
Debt Instrument [Line Items]              
Applicable margin added     0.975%        
Revolving Credit Facility [Member] | WES RCF [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Western Gas Partners, LP [Member]              
Debt Instrument [Line Items]              
Applicable margin added     1.45%