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Derivatives Financial Instruments - Derivative Income Statement Location (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Derivative [Line Items]        
Total gain (loss) $ 1 $ (16) $ 14 $ (20)
Product Sales [Member]        
Derivative [Line Items]        
Realized gain (loss) 0 (1) (1) 6
Unrealized gain (loss) 2 (6) 9 (14)
Total gain (loss) 2 (7) 8 (8)
Purchased product costs [Member]        
Derivative [Line Items]        
Realized gain (loss) (2) (2) (4) (3)
Unrealized gain (loss) 1 (8) 10 (9)
Total gain (loss) (1) (10) 6 (12)
Cost of Sales [Member]        
Derivative [Line Items]        
Realized gain (loss) 0 (1) 0 (2)
Unrealized gain (loss) 0 2 0 2
Total gain (loss) $ 0 $ 1 $ 0 $ 0