Income Taxes Summary of Positions for Which Significant Change in Unrecognized Tax Benefits is Reasonable Possible (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Unrecognized Tax Benefit Begin of Period	Dec. 31, 2011 Unrecognized Tax Benefit Begin of Period	Dec. 31, 2009 Unrecognized Tax Benefit Begin of Period	Dec. 31, 2012 Unrecognized Tax Benefit End of Period	Dec. 31, 2011 Unrecognized Tax Benefit End of Period	Dec. 31, 2010 Unrecognized Tax Benefit End of Period
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized Tax Benefits, Beginning of Period	$ 369			$ 369	$ 34	$ 231	$ 599	$ 369	$ 34
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	134	135	0
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	96	200	(197)
Unrecognized Tax Benefits, Increases Resulting from Settlements with Taxing Authorities	0	0	0
Unrecognized Tax Benefits, End of Period	$ 599	$ 369		$ 369	$ 34	$ 231	$ 599	$ 369	$ 34