Variable Interest Entities (Settlement Payments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Settlement Payments Mark To Market Adjustments Variable Interest Entity	$ 163	$ (82)
Number of CLN structures invested in and consolidated by the company	2
Percent of outstanding notes of the CLN structures invested in by the company and third parties	100.00%
Credit default swaps [Member]
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Settlement Payments Mark To Market Adjustments Variable Interest Entity	166	(80)
Contingent Forwards [Member]
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Settlement Payments Mark To Market Adjustments Variable Interest Entity	$ (3)	$ (2)