v2.4.0.6
Fair Value Measurement - FV Hierarchy (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments $ 309 $ 305
Commodity derivatives - assets, gross 1,497 1,637
Total assets 1,806 1,942
Commodity derivatives - liabilities, gross 1,552 1,602
Total liabilities 1,552 1,602
Level 1 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation investments 309 305
Commodity derivatives - assets, gross 972 1,052
Total assets 1,281 1,357
Commodity derivatives - liabilities, gross 990 1,031
Total liabilities 990 1,031
Level 2 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivatives - assets, gross 512 567
Total assets 512 567
Commodity derivatives - liabilities, gross 561 567
Total liabilities 561 567
Level 3 [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivatives - assets, gross 13 18
Total assets 13 18
Commodity derivatives - liabilities, gross 1 4
Total liabilities $ 1 $ 4