Financial Guaranty Insurance Premiums (Details 6) (USD $) In Millions, unless otherwise specified							3 Months Ended	12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012	Sep. 30, 2012		Dec. 31, 2011	Sep. 30, 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	$ 906	[1]	$ 1,005	$ 944	[1]	$ 1,003	$ 906	$ 1,005
Gross deferred premium revenue	$ 4,793		$ 5,356				$ 1,647	$ 1,908
Weighted-average risk-free rate used to discount premiums (as a percent)							3.40%	3.50%
Weighted-average period of premiums receivable (in years)							9 years 6 months	9 years 7 months 6 days

[1] Excludes $19 million and $30 million as of September 30, 2013 and September 30, 2012, respectively, related to consolidated FG VIEs.