v3.20.2
Fair Value Measurement - FV Hierarchy (Details) - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment in Cenovus Energy $ 809 $ 2,111
Investments in debt securities 482 241
Commodity derivative asset, gross 301 322
Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment in Cenovus Energy 809 2,111
Investments in debt securities 482 241
Commodity derivative asset, gross 301 322
Total assets 1,592 2,674
Commodity derivative liability, gross 277 311
Total liabilities 277 311
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment in Cenovus Energy 809 2,111
Investments in debt securities 21 25
Commodity derivative asset, gross 173 172
Total assets 1,003 2,308
Commodity derivative liability, gross 173 174
Total liabilities 173 174
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment in Cenovus Energy 0 0
Investments in debt securities 461 216
Commodity derivative asset, gross 117 114
Total assets 578 330
Commodity derivative liability, gross 89 115
Total liabilities 89 115
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment in Cenovus Energy 0 0
Investments in debt securities 0 0
Commodity derivative asset, gross 11 36
Total assets 11 36
Commodity derivative liability, gross 15 22
Total liabilities $ 15 $ 22