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Debt and Interest Expense - Additional Information (Detail) - USD ($)
9 Months Ended
Sep. 30, 2015
Jan. 23, 2015
Dec. 31, 2014
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 17,497,000,000   $ 16,687,000,000
Commercial Paper [Member]      
Debt Instrument [Line Items]      
Line of credit, maximum capacity 3,000,000,000    
Commercial paper, outstanding borrowings $ 547,000,000    
Commercial paper, weighted-average interest rate 0.51%    
Amount of current debt outstanding classified as long-term debt on the Company's Consolidated Balance Sheet $ 547,000,000    
Commercial Paper [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Debt instrument, term 397 days    
Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member]      
Debt Instrument [Line Items]      
Estimated fair value of total borrowings $ 17,200,000,000   $ 17,400,000,000
5.950% Senior Notes Due 2016 [Member] | Senior Notes [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 1,750,000,000    
Debt instrument, stated interest rate 5.95%    
Debt instrument, maturity date Sep. 15, 2016    
Amount of current debt outstanding classified as long-term debt on the Company's Consolidated Balance Sheet $ 1,750,000,000    
Five-Year Credit Facility [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Line of credit, maximum capacity $ 3,000,000,000    
Debt instrument, term 5 years    
Line of credit, expandable maximum capacity $ 4,000,000,000    
Line of credit, outstanding borrowings $ 0    
Five-Year Credit Facility [Member] | Revolving Credit Facility [Member] | Minimum [Member]      
Debt Instrument [Line Items]      
Applicable margin added 0.00%    
Five-Year Credit Facility [Member] | Revolving Credit Facility [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Applicable margin added 1.65%    
Ratio of indebtedness to total capital 0.65    
Zero-Coupon Senior Notes [Member] | Senior Notes [Member]      
Debt Instrument [Line Items]      
Debt instrument, maturity date Oct. 10, 2036    
Debt Instrument, earliest call date Oct. 10, 2015    
Zero-Coupon Senior Notes [Member] | Senior Notes [Member] | Accreted Value at Next Potential Put Date [Member]      
Debt Instrument [Line Items]      
Debt instrument, accreted value $ 796,000,000    
$5.0 billion Facility [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Line of credit, maximum capacity   $ 5,000,000,000  
364-Day Credit Facility [Member] | Revolving Credit 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 Credit Facility [Member] | Revolving Credit Facility [Member] | Minimum [Member]      
Debt Instrument [Line Items]      
Applicable margin added 0.00%    
364-Day Credit Facility [Member] | Revolving Credit Facility [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Applicable margin added 1.675%    
Ratio of indebtedness to total capital 0.65    
WES 3.950% Senior Notes Due 2025 [Member] | Senior Notes [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Debt instrument, principal amount $ 500,000,000    
Debt instrument, stated interest rate 3.95%    
Debt instrument, maturity date May 15, 2025    
WES RCF [Member] | Revolving Credit Facility [Member] | Western Gas Partners, LP [Member]      
Debt Instrument [Line Items]      
Line of credit, maximum capacity $ 1,200,000,000    
Line of credit, expandable maximum capacity 1,500,000,000    
Line of credit, outstanding borrowings $ 180,000,000    
Line of credit, expiration date Feb. 26, 2019    
Line of credit, interest rate 1.50%    
Letters of credit, outstanding $ 13,000,000    
Line of credit, available borrowing capacity $ 1,000,000,000