Property, Plant and Equipment (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Unproved Oil and Natural Gas Properties      
Total property, plant and equipment, net $ 8,915,000,000   $ 8,728,000,000
Restructuring Cost and Reserve [Line Items]      
Property, plant, and equipment associated with unproven oil and natural gas properties 500,000,000   700,000,000
Transfer from unproved properties to proved properties 200,000,000    
Amortization of unproved leasehold costs 4,000,000 7,000,000  
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Projected inflation rate (as a percent) 2.50%    
Changes in net asset retirement liability      
Net asset retirement liability at January 1 42,000,000    
Liabilities incurred 1,000,000    
Liabilities settled (1,000,000)    
Accretion expense 1,000,000    
Net asset retirement liability at March 31, 2015 43,000,000    
Capitalized Interest      
Capitalized interest 4,000,000 5,000,000  
Minimum      
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Credit-adjusted risk-free rate (as a percent) 7.00%    
Maximum      
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Credit-adjusted risk-free rate (as a percent) 9.00%    
Wolfcamp      
Restructuring Cost and Reserve [Line Items]      
Property, plant, and equipment associated with unproven oil and natural gas properties 400,000,000    
Altamont      
Restructuring Cost and Reserve [Line Items]      
Property, plant, and equipment associated with unproven oil and natural gas properties $ 100,000,000