Schedule II - Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 5	$ 7	$ 14
Charged to costs and expenses	2	1	(6)
Charged to other accounts	0	0	0
Deductions	(1)	(3)	(1)
Balance at end of period	6	5	7
Cash discounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	3	2	1
Charged to costs and expenses	34	34	37
Charged to other accounts	0	0	0
Deductions	(34)	(33)	(36)
Balance at end of period	3	3	2
Income tax valuation allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	51	70	1,023
Charged to costs and expenses	124	0	0
Charged to other accounts	0	0	0
Deductions	0	(19)	(953)
Balance at end of period	$ 175	$ 51	$ 70