Financial Guaranty Insurance Losses (Loss and LAE Reported on the Statements of Operations) (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Guarantor Obligations [Line Items]
Subtotal	$ (55)	$ 250
Effect of consolidating FG VIEs	7	(8)
Loss and LAE	(48)	242
Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(55)	250
Other
Guarantor Obligations [Line Items]
Subtotal	0	0
Prime first lien | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	0	0
Alt-A first lien | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	9	(1)
First mortgage, option adjustable rate mortgage | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(83)	52
First mortgage, subprime | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	11	8
Total first lien | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(63)	59
Close ended second lien | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	20	(1)
HELOCs | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	3	15
Second lien | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	23	14
U.S. RMBS | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(40)	73
TruPS | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	0	(4)
Other structured finance | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(12)	(28)
US Public Finance | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	(4)	19
Public finance Non-U.S. | Financial guaranty
Guarantor Obligations [Line Items]
Subtotal	$ 1	$ 190