Financial Guaranty Insurance Premiums (Selected Information for Policies Paid in Installments) (Details 7) (USD $) In Millions, unless otherwise specified							3 Months Ended	12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012	Mar. 31, 2012		Dec. 31, 2011	Mar. 31, 2013 Policies Paid in Installments	Dec. 31, 2012 Policies Paid in Installments
Financial Guaranty Insurance Premiums [Line Items]
Premiums receivable, net of ceding commissions payable	$ 956	[1]	$ 1,005	$ 1,019	[1]	$ 1,003	$ 956	$ 1,005
Deferred premium revenue, gross	$ 5,097		$ 5,356				$ 1,788	$ 1,908
Weighted-average risk-free rate used to discount premiums (as a percent)							3.60%	3.50%
Weighted-average period of premiums receivable (in years)							9 years 6 months	9 years 7 months 6 days

[1] )Excludes $28 million and $33 million as of March 31, 2013 and March 31, 2012, respectively, related to consolidated FG VIEs.