Expected Losses to be Paid (Present Value of Net Expected Loss to be Paid Before Recoveries for Breaches of R&W) (Details 1) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					3 Months Ended																																																									12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012	Mar. 31, 2013 Prime first lien		Mar. 31, 2012 Prime first lien		Mar. 31, 2013 Alt-A first lien		Mar. 31, 2012 Alt-A first lien		Mar. 31, 2013 First mortgage, option adjustable rate mortgage		Mar. 31, 2012 First mortgage, option adjustable rate mortgage		Mar. 31, 2013 First mortgage, subprime		Mar. 31, 2012 First mortgage, subprime		Mar. 31, 2013 Total first lien		Mar. 31, 2012 Total first lien		Mar. 31, 2013 Closed end second lien and HELOCs		Mar. 31, 2012 Closed end second lien and HELOCs		Mar. 31, 2013 HELOCs		Mar. 31, 2012 HELOCs		Mar. 31, 2013 Second lien		Mar. 31, 2012 Second lien		Mar. 31, 2013 U.S. RMBS		Mar. 31, 2012 U.S. RMBS		Mar. 31, 2013 TruPS		Mar. 31, 2012 TruPS		Mar. 31, 2013 Other structured finance		Mar. 31, 2012 Other structured finance		Mar. 31, 2013 US Public Finance		Mar. 31, 2012 US Public Finance		Mar. 31, 2013 Public finance Non-U.S.		Mar. 31, 2012 Public finance Non-U.S.		Mar. 31, 2013 Other		Mar. 31, 2012 Other		Mar. 31, 2013 Minimum	Dec. 31, 2012 Minimum	Mar. 31, 2013 Maximum	Dec. 31, 2012 Maximum
Guarantor Obligations [Line Items]
Discount factor (as a percent)																																																														0.00%	0.00%	3.72%	3.28%
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid Before Recoveries for R&W	$ 2,047	[1]	$ 2,756			$ 10	[1]	$ 5		$ 693	[1]	$ 702		$ 460	[1]	$ 935		$ 351	[1]	$ 342		$ 1,514	[1]	$ 1,984		$ 99	[1]	$ 138		$ 39	[1]	$ 159		$ 138	[1]	$ 297		$ 1,652	[1]	$ 2,281		$ 27	[1]	$ 64		$ 312	[1]	$ 342		$ 7	[1]	$ 16		$ 52	[1]	$ 51		$ (3)	[1]	$ 2
Net Expected Loss Development Before Recoveries for R&W	59		263			6		1		1		25		15		26		29		11		51		63		(8)		(5)		14		10		6		5		57		68		(3)		(4)		(2)		(22)		7		23		10		198		(10)		0
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid Before Recoveries for R&W	(181)	[2]	(203)	[1]		(1)	[2]	0	[1]	(19)	[2]	(26)	[1]	(112)	[2]	(107)	[1]	(4)	[2]	(9)	[1]	(136)	[2]	(142)	[1]	(4)	[2]	(12)	[1]	(14)	[2]	(71)	[1]	(18)	[2]	(83)	[1]	(154)	[2]	(225)	[1]	(1)	[2]	(2)	[1]	(3)	[2]	(24)	[1]	(23)	[2]	(6)	[1]	0	[2]	54	[1]	0	[2]	0	[1]
End of Period, Net Expected Loss to be Paid Before Recoveries for R&W	1,925	[1]	2,816			15	[1]	6		675	[1]	701		363	[1]	854		376	[1]	344		1,429	[1]	1,905		87	[1]	121		39	[1]	98		126	[1]	219		1,555	[1]	2,124		23	[1]	58		307	[1]	296		(9)	[1]	33		62	[1]	303		(13)	[1]	2
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)	45 days
Expected LAE for mitigating claim liabilities	31				39
Financial Guarantee Insurance Contracts, Risk Management Activities, Mitigating Claim Liabilities, Expense	$ 13		$ 9

[1] Net of ceded paid losses, whether or not such amounts have been settled with reinsurers. Ceded paid losses are typically settled 45 days after the end of the reporting period. Such amounts are recorded in reinsurance recoverable on paid losses included in other assets.

[2] Excludes $18 million and $17 million for First Quarter 2013 and 2012, respectively, related to consolidated FG VIEs.