Schedule II Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Allowance for Trade Receivables [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 24		$ 25		$ 23
Additions Charged To Income	15		25		30
Additions Charged to Other Accounts	0		0		0
Deductions From Reserves	16	[1]	26	[1]	28	[1]
Balance at End of Period	23		24		25
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	3		3		5
Additions Charged To Income	(1)		0		(2)
Additions Charged to Other Accounts	0	[1]	0		0
Deductions From Reserves			0	[1]	0	[1]
Balance at End of Period	$ 2		$ 3		$ 3

[1] Deductions from reserves represent losses or expenses for which the respective reserves were created. In the case of the uncollectible accounts reserve, such deductions are net of recoveries of amounts previously written off.