Financial Guaranty Insurance Losses (Details 7) (USD $)	3 Months Ended
	Jun. 30, 2013
AGM
Guarantor Obligations [Line Items]
Maximum possible estimated termination payment on swap obligations after taking account the rating downgrade in January 2013	$ 118,000,000
Maximum possible estimated termination payment on swap obligations after taking account the possibility of further rating downgrades	332,000,000
Variable rate demand obligations
Guarantor Obligations [Line Items]
Rate basis for bank bond rate	prime rate
Variable rate demand obligations | AGM and AGC
Guarantor Obligations [Line Items]
Financial guaranty insurance contracts principal amount insured	8,200,000,000
Financial Guaranty Insurance Contracts, Principal Amount BBB- or below	$ 400,000,000
Minimum | Variable rate demand obligations
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	2.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	90 days
Maximum | Variable rate demand obligations
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	3.00%
Bank bond capped rate (as a percent)	25.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	180 days
Cash | Minimum
Guarantor Obligations [Line Items]
Collaterlization as a Percentage of GIC Balance	100.00%
Asset-backed securities | Maximum
Guarantor Obligations [Line Items]
Collaterlization as a Percentage of GIC Balance	108.00%