Expected Losses to be Paid (Present Value of Net Expected Loss to be Paid) (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ 677	[1]	$ 1,106
Net Expected Loss Development After Recoveries for R&W	(98)		212
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(92)	[1]	(133)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	487		1,185
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
Prime first lien
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	6	[1]	2
Net Expected Loss Development After Recoveries for R&W	6		0
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(1)	[1]	0	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	11		2
Alt-A first lien
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	315	[1]	295
Net Expected Loss Development After Recoveries for R&W	9		(2)
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(11)	[1]	(25)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	313		268
First mortgage, option adjustable rate mortgage
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(131)	[1]	210
Net Expected Loss Development After Recoveries for R&W	(138)		(2)
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(58)	[1]	(89)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(327)		119
First mortgage, subprime
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	242	[1]	241
Net Expected Loss Development After Recoveries for R&W	25		16
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(4)	[1]	(9)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	263		248
Total first lien
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	432	[1]	748
Net Expected Loss Development After Recoveries for R&W	(98)		12
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(74)	[1]	(123)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	260		637
Close ended second lien
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(39)	[1]	(86)
Net Expected Loss Development After Recoveries for R&W	1		(3)
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	17	[1]	(12)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(21)		(101)
HELOCs
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(111)	[1]	(31)
Net Expected Loss Development After Recoveries for R&W	(3)		8
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(8)	[1]	(20)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(122)		(43)
Second lien
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(150)	[1]	(117)
Net Expected Loss Development After Recoveries for R&W	(2)		5
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	9	[1]	(32)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(143)		(144)
U.S. RMBS
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	282	[1]	631
Net Expected Loss Development After Recoveries for R&W	(100)		17
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(65)	[1]	(155)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	117		493
TruPS
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	27	[1]	64
Net Expected Loss Development After Recoveries for R&W	(3)		(4)
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(1)	[1]	(2)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	23		58
Other structured finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	312	[1]	342
Net Expected Loss Development After Recoveries for R&W	(2)		(22)
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(3)	[1]	(24)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	307		296
US Public Finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	7	[1]	16
Net Expected Loss Development After Recoveries for R&W	7		23
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	(23)	[1]	(6)	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(9)		33
Public finance Non-U.S.
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	52	[1]	51
Net Expected Loss Development After Recoveries for R&W	10		198
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	0	[1]	54	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	62		303
Other
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	(3)	[1]	2
Net Expected Loss Development After Recoveries for R&W	(10)		0
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid After Recoveries for R&W	0	[1]	0	[1]
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ (13)		$ 2

[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.