Income Taxes (Schedule of Unrecognized tax benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012
Schedule of Unrecognized Tax Benefits [Abstract]
Balance, January 1	$ 190	$ 157	$ 119	$ 43
Additions for tax positions of the current year	9	2	41
Additions for tax positions of prior years	10	83	25
Reductions for tax positions of prior years	(24)	(50)	(16)
Settlements during the period	(1)	(1)	(2)
Lapses of applicable statute of limitation	(6)	(1)	(10)
Balance, December 31	$ 178	$ 190	$ 157	$ 43