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Derivatives - Effect of Commodity Derivative Instruments in Statements of Income (Detail) - Commodity derivatives - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2017
Sep. 30, 2019
Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]        
Loss $ 49 $ (66) $ (33) $ (151)
Sales and other operating revenues        
Derivative Instruments, Gain (Loss) [Line Items]        
Loss (1) 3 (18) 1
Cost of revenues        
Derivative Instruments, Gain (Loss) [Line Items]        
Loss $ 50 $ (69) $ (15) $ (152)