Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Valuation And Qualifying Accounts Disclosure[ Line Items]
Valuation Allowances And Reserves Balance	$ 17	$ 16	$ 14
Valuation Allowances And Reserves Charged To Cost And Expense	20
Valuation Allowances And Reserves Charged To Other Accounts	0
Allowance For Doubtful Accounts [Member]
Valuation And Qualifying Accounts Disclosure[ Line Items]
Valuation Allowances And Reserves Balance			14	16
Valuation Allowances And Reserves Charged To Cost And Expense		22	25
Valuation Allowances And Reserves Deductions	(19)	(20)	(27)
Valuation Allowances And Reserves Charged To Other Accounts		0	0
Valuation Allowance Of Deferred Tax Assets [Member]
Valuation And Qualifying Accounts Disclosure[ Line Items]
Valuation Allowances And Reserves Balance	3	3	3	3
Valuation Allowances And Reserves Charged To Cost And Expense	0	0	0
Valuation Allowances And Reserves Deductions	0	0	0
Valuation Allowances And Reserves Charged To Other Accounts	$ 0	$ 0	$ 0