Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Beginning Balance	$ 33	$ 39	$ 29
Additions for tax positions of prior years	6	1	9
Reductions for tax positions of prior years	(2)	(15)	(7)
Additions based on tax positions related to the current year	9	9	20
Settlements	(1)		(10)
Lapse of statute of limitations	(3)	(1)	(2)
Ending Balance	$ 42	$ 33	$ 39