Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) - Parenthetical (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Equity [Abstract]
Tax on unrealized gains and losses of derivatives	$ 20	$ 29
Tax on reclassification adjustments	73	3
Tax on unrealized holding gains	0	(5)
Tax on reclassification adjustment for gains realized in net income	(62)	0
Tax on reclassification adjustment for gains on net income	(1)	0
Tax on transaction gains (losses)	(1)		1
Tax on translation gain and loss	$ (9)	$ 0