v2.4.0.6
Fair Value Measurement (Details) (Fair Value, Measurements, Recurring [Member], USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments $ 309 $ 336
Commodity derivative asset, gross 2,609 4,826
Total assets 2,918 5,162
Commodity derivative liability, gross 2,570 4,702
Total liabilities 2,570 4,702
Level 1 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments 309 336
Commodity derivative asset, gross 1,788 2,807
Total assets 2,097 3,143
Commodity derivative liability, gross 1,749 2,970
Total liabilities 1,749 2,970
Level 2 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments 0 0
Commodity derivative asset, gross 803 1,947
Total assets 803 1,947
Commodity derivative liability, gross 814 1,722
Total liabilities 814 1,722
Level 3 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments 0 0
Commodity derivative asset, gross 18 72
Total assets 18 72
Commodity derivative liability, gross 7 10
Total liabilities $ 7 $ 10