Financial Guaranty Insurance Premiums (Components of Unearned Premium Reserve) (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Financial Guaranty Insurance Premiums [Line Items]
Deferred premium revenue, gross	$ 5,097		$ 5,356
Deferred premium revenue, ceded	558		586
Deferred premium revenue, net	4,539	[1]	4,770	[1]	5,279	5,327
Unearned premium reserve	4,982		5,207
Prepaid Reinsurance Premiums	535		561
Unearned Premiums, Net	4,447	[1]	4,646	[1]
Total net unearned premium reserve related to FG VIE	244		262
Contra-paid related to FG and VIEs	72		98
Financial guaranty
Financial Guaranty Insurance Premiums [Line Items]
Deferred premium revenue, gross	5,090		5,349
Deferred premium revenue, ceded	558		586
Deferred premium revenue, net	4,532	[1]	4,763	[1]
Contra-paid, gross	(115)		(149)
Contra-paid, ceded	(23)		(25)
Contra-paid, net	(92)	[1]	(124)	[1]
Other
Financial Guaranty Insurance Premiums [Line Items]
Unearned premium reserve	7		7
Prepaid Reinsurance Premiums	0		0
Unearned Premiums, Net	$ 7	[1]	$ 7	[1]

[1] (1)Excludes $244 million and $262 million of deferred premium revenue, and $72 million and $98 million of contra-paid related to FG VIEs as of March 31, 2013 and December 31, 2012, respectively.