Revision of Previously Issued Financial Statements - Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income	$ 15	$ 98	$ 88	$ 170
Deferred income taxes	(7)	9	0	12
Increase (decrease) in payables	(7)	7	86	64
Changes in long-term liabilities	$ 2	8	$ 7	2
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income		103		175
Deferred income taxes		10		13
Increase (decrease) in payables		6		62
Changes in long-term liabilities		3		(2)
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income		(5)		(5)
Deferred income taxes		(1)		(1)
Increase (decrease) in payables		1		2
Changes in long-term liabilities		$ 5		$ 4