v3.7.0.1
Fair Value Measurement - FV Hierarchy (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivative asset, gross $ 251 $ 312
Total assets 251 312
Commodity derivative liability, gross 237 334
Total liabilities 237 334
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivative asset, gross 135 194
Total assets 135 194
Commodity derivative liability, gross 152 207
Total liabilities 152 207
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivative asset, gross 95 96
Total assets 95 96
Commodity derivative liability, gross 70 105
Total liabilities 70 105
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity derivative asset, gross 21 22
Total assets 21 22
Commodity derivative liability, gross 15 22
Total liabilities $ 15 $ 22