Allowance for Loan Losses and Reserve for Guaranty Losses Reserve for Guaranty Losses (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reserve for Guaranty Losses [Roll Forward]
Beginning balance, January 1	$ 994	$ 323	$ 54,430
Provision for guaranty losses	339	804	194
Charge-offs	(174)	(138)	(203)
Recoveries	72	5	5
Ending balance, December 31	1,231	994	323
Consolidation Acounting Guidance Adopted on January 1, 2010 [Member]
Reserve for Guaranty Losses [Roll Forward]
Adoption of consolidation accounting guidance			$ (54,103)