Financial Guaranty Insurance Losses - Loss and LAE Reported on the Statements of Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE	$ 72	$ (44)	$ 57	$ 41	$ 85	$ 55	$ 62	$ (48)	$ 126	$ 154	$ 504
Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									156	175	569
Variable Interest Entity, Primary Beneficiary [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(30)	(21)	(65)
Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									157	175	586
Other Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(1)	0	(17)
RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(129)	(4)	308
TruPS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(1)	(1)	(10)
Other structured finance [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									96	(34)	3
Structured Finance [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(34)	(39)	301
Public Finance [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									191	214	285
Public Finance [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									192	198	51
Public Finance [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | Non United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(1)	16	234
First Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(96)	31	228
Second Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(33)	(35)	80
Prime [Member] | First Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(1)	1	2
Alt-A [Member] | First Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(66)	(2)	51
Option ARM [Member] | First Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(37)	(48)	137
Subprime [Member] | First Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									8	80	38
Closed-end [Member] | Second Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									(2)	18	31
HELOCs [Member] | Second Lien [Member] | RMBS [Member] | Financial Guarantee Insurance Product Line [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | United States [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE									$ (31)	$ (53)	$ 49