Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 10	$ 14	$ 15
Charged to costs and expenses	9	0	7
Charged to other accounts	1	1	0
Deductions	0	(5)	(8)
Balance at end of period	20	10	14
Cash discounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	2	2	2
Charged to costs and expenses	45	42	38
Charged to other accounts	0	0	0
Deductions	(45)	(42)	(38)
Balance at end of period	2	2	2
Income tax valuation allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	995	1,125	1,042
Charged to costs and expenses	1	(2)	1
Charged to other accounts	112	0	82
Deductions	(85)	(128)	0
Balance at end of period	$ 1,023	$ 995	$ 1,125