Expected Losses to be Paid (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Jun. 30, 2013	Dec. 31, 2012		Jun. 30, 2012	Dec. 31, 2011
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	$ 809				$ 809					$ 680
Net Expected Loss to be Paid After Recoveries for R&W	806	[1]	753	[1]	806	[1]	753	[1]	774	677	[1]	1,198	1,106
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(22)		64		(23)		371
Net Expected Loss Development After Recoveries for R&W	(22)		64		(33)		365
Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	552				552					451
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(25)		171		(27)		374
Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	52	[2]			52	[2]				(96)	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	14	[2]	(118)	[2]	(18)	[2]	(20)	[2]
Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	205				205					325
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(11)	[3]	11	[3]	22	[3]	17	[3]
Prime first lien
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	21				21					6
Net Expected Loss to be Paid After Recoveries for R&W	21	[1]	5	[1]	21	[1]	5	[1]	18	6	[1]	4	2
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	3		1		16		3
Net Expected Loss Development After Recoveries for R&W	3		1		16		3
Prime first lien | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	3				3					4
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0		1		(1)		2
Prime first lien | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	0	[2]			0	[2]				0	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[2]	0	[2]	0	[2]	0	[2]
Prime first lien | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	18				18					2
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	3	[3]	0	[3]	17	[3]	1	[3]
Alt-A first lien
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	206				206					315
Net Expected Loss to be Paid After Recoveries for R&W	206	[1]	311	[1]	206	[1]	311	[1]	288	315	[1]	321	295
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(85)		14		(83)		27
Net Expected Loss Development After Recoveries for R&W	(85)		14		(83)		27
Alt-A first lien | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	90				90					164
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(53)		38		(60)		30
Alt-A first lien | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	29	[2]			29	[2]				27	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	3	[2]	(34)	[2]	3	[2]	(12)	[2]
Alt-A first lien | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	87				87					124
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(35)	[3]	10	[3]	(26)	[3]	9	[3]
Option ARM
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	7				7					(131)
Net Expected Loss to be Paid After Recoveries for R&W	7	[1]	(90)	[1]	7	[1]	(90)	[1]	(20)	(131)	[1]	3	210
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	25		3		(92)		12
Net Expected Loss Development After Recoveries for R&W	25		3		(92)		12
Option ARM | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(14)				(14)					(114)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	20		(69)		(58)		15
Option ARM | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	11	[2]			11	[2]				(37)	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	1	[2]	76	[2]	(32)	[2]	(9)	[2]
Option ARM | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	10				10					20
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	4	[3]	(4)	[3]	(2)	[3]	6	[3]
First mortgage, subprime
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	303				303					242
Net Expected Loss to be Paid After Recoveries for R&W	303	[1]	239	[1]	303	[1]	239	[1]	274	242	[1]	236	241
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	38		13		86		39
Net Expected Loss Development After Recoveries for R&W	38		13		86		39
First mortgage, subprime | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	144				144					118
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	25		32		40		29
First mortgage, subprime | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	73	[2]			73	[2]				50	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	5	[2]	(21)	[2]	25	[2]	4	[2]
First mortgage, subprime | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	86				86					74
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	8	[3]	2	[3]	21	[3]	6	[3]
Total first lien
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	537				537					432
Net Expected Loss to be Paid After Recoveries for R&W	537	[1]	465	[1]	537	[1]	465	[1]	560	432	[1]	564	748
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(19)		31		(73)		81
Net Expected Loss Development After Recoveries for R&W	(19)		31		(73)		81
Total first lien | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	223				223					172
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(8)		2		(79)		76
Total first lien | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	113	[2]			113	[2]				40	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	9	[2]	21	[2]	(4)	[2]	(17)	[2]
Total first lien | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	201				201					220
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(20)	[3]	8	[3]	10	[3]	22	[3]
Close ended second lien
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(13)				(13)					(39)
Net Expected Loss to be Paid After Recoveries for R&W	(13)	[1]	(25)	[1]	(13)	[1]	(25)	[1]	(14)	(39)	[1]	(29)	(86)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0		4		7		0
Net Expected Loss Development After Recoveries for R&W	0		4		7		0
Close ended second lien | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(36)				(36)					(60)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	2		63		0		4
Close ended second lien | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	25	[2]			25	[2]				31	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(3)	[2]	(64)	[2]	(4)	[2]	(9)	[2]
Close ended second lien | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(2)				(2)					(10)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	1	[3]	5	[3]	11	[3]	5	[3]
HELOCs
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(129)				(129)					(111)
Net Expected Loss to be Paid After Recoveries for R&W	(129)	[1]	(107)	[1]	(129)	[1]	(107)	[1]	(97)	(111)	[1]	(64)	(31)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(42)		(13)		(76)		9
Net Expected Loss Development After Recoveries for R&W	(42)		(13)		(76)		9
HELOCs | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(43)				(43)					56
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(49)		62		(66)		3
HELOCs | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(86)	[2]			(86)	[2]				(167)	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	8	[2]	(75)	[2]	(10)	[2]	6	[2]
HELOCs | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	0				0					0
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(1)	[3]	0	[3]	0	[3]	0	[3]
Second lien
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(142)				(142)					(150)
Net Expected Loss to be Paid After Recoveries for R&W	(142)	[1]	(132)	[1]	(142)	[1]	(132)	[1]	(111)	(150)	[1]	(93)	(117)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(42)		(9)		(69)		9
Net Expected Loss Development After Recoveries for R&W	(42)		(9)		(69)		9
Second lien | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(79)				(79)					(4)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(47)		125		(66)		7
Second lien | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	(61)	[2]			(61)	[2]				(136)	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	5	[2]	(139)	[2]	(14)	[2]	(3)	[2]
Second lien | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(2)				(2)					(10)
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[3]	5	[3]	11	[3]	5	[3]
U.S. RMBS
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	395				395					282
Net Expected Loss to be Paid After Recoveries for R&W	395	[1]	333	[1]	395	[1]	333	[1]	449	282	[1]	471	631
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(61)		22		(142)		90
Net Expected Loss Development After Recoveries for R&W	(61)		22		(142)		90
U.S. RMBS | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	144				144					168
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(55)		127		(145)		83
U.S. RMBS | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	52	[2]			52	[2]				(96)	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	14	[2]	(118)	[2]	(18)	[2]	(20)	[2]
U.S. RMBS | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	199				199					210
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(20)	[3]	13	[3]	21	[3]	27	[3]
TruPS
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	50				50					27
Net Expected Loss to be Paid After Recoveries for R&W	50	[1]	53	[1]	50	[1]	53	[1]	33	27	[1]	50	64
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	9		5		7		(6)
Net Expected Loss Development After Recoveries for R&W	9		5		7		(6)
TruPS | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	4				4					1
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	1		3		1		(3)
TruPS | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	0	[2]			0	[2]				0	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[2]	0	[2]	0	[2]	0	[2]
TruPS | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	46				46					26
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	8	[3]	2	[3]	6	[3]	(3)	[3]
Structured finance
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	128				128					312
Net Expected Loss to be Paid After Recoveries for R&W	128	[1]	315	[1]	128	[1]	315	[1]	158	312	[1]	320	342
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(13)		(3)		(39)		7
Net Expected Loss Development After Recoveries for R&W	(13)		(3)		(39)		7
Structured finance | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	170				170					224
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(13)		0		(32)		12
Structured finance | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	0	[2]			0	[2]				0	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[2]	0	[2]	0	[2]	0	[2]
Structured finance | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	(42)				(42)					88
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[3]	(3)	[3]	(7)	[3]	(5)	[3]
US Public Finance
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	183				183					7
Net Expected Loss to be Paid After Recoveries for R&W	183	[1]	10	[1]	183	[1]	10	[1]	71	7	[1]	59	16
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	44		7		138		65
Net Expected Loss Development After Recoveries for R&W	44		7		138		65
US Public Finance | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	183				183					7
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	43		8		137		66
US Public Finance | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	0	[2]			0	[2]				0	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[2]	0	[2]	0	[2]	0	[2]
US Public Finance | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	0				0					0
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	1	[3]	(1)	[3]	1	[3]	(1)	[3]
Public finance Non-U.S.
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	53				53					52
Net Expected Loss to be Paid After Recoveries for R&W	53	[1]	46	[1]	53	[1]	46	[1]	66	52	[1]	302	51
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(1)		33		13		215
Net Expected Loss Development After Recoveries for R&W	(1)		33		13		215
Public finance Non-U.S. | Financial guaranty
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	51				51					51
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	(1)		33		12		216
Public finance Non-U.S. | Financial Guaranty Variable Interest Entities
Guarantor Obligations [Line Items]
Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability	0	[2]			0	[2]				0	[2]
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[2]	0	[2]	0	[2]	0	[2]
Public finance Non-U.S. | Credit Default Swap
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W Excluding Other Lines of Business	2				2					1
Net Expected Loss Development After Recoveries for R&W Excluding Other Lines of Business	0	[3]	0	[3]	1	[3]	(1)	[3]
Other
Guarantor Obligations [Line Items]
Net Expected Loss to be Paid After Recoveries for R&W	(3)				(3)					(3)
Net Expected Loss Development After Recoveries for R&W	$ 0		$ 0		$ (10)		$ (6)

[1] Includes net expected loss adjustment expenses ("LAE") to be paid for mitigating claim liabilities of $34 million as of September 30, 2013 and $39 million as of December 31, 2012. The Company paid $12 million and $14 million in LAE for Third Quarter 2013 and 2012, respectively, and $41 million and $33 million in LAE for Nine Months 2013 and 2012, respectively.

[2] Refer to Note 9, Consolidation of Variable Interest Entities.

[3] Refer to Note 8, Financial Guaranty Contracts Accounted for as Credit Derivatives.