Financial Guaranty Insurance Losses - Loss and LAE Reserve and Salvage and Subrogation Recoverable Net of Reinsurance (Details) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE Reserve, net	[1]	$ 918	$ 721
Salvage and Subrogation Recoverable, net	[1]	136	154
(in millions)	[1]	782	567
Financial Guarantee Insurance And Other Product Line [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE Reserve, net		899
Financial Guarantee Insurance And Other 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 Reserve, net		991	801
Salvage and Subrogation Recoverable, net		137	155
(in millions)		854	646
Financial Guarantee Insurance And Other Product Line [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and LAE Reserve, net		(73)	(80)
Salvage and Subrogation Recoverable, net		(1)	(1)
(in millions)		(72)	(79)
Public Finance [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		555	273
Salvage and Subrogation Recoverable, net		11	8
(in millions)		544	265
Triple-X Life Insurance Transaction [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		80	140
Salvage and Subrogation Recoverable, net		0	0
(in millions)		80	140
Trust Preferred Securities (TruPS) [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		0	0
Salvage and Subrogation Recoverable, net		0	0
(in millions)		0	0
Student Loan [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		53	64
Salvage and Subrogation Recoverable, net		0	0
(in millions)		53	64
Other structured finance [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		47	34
Salvage and Subrogation Recoverable, net		0	8
(in millions)		47	26
Structured Finance [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		436	528
Salvage and Subrogation Recoverable, net		121	134
(in millions)		315	394
Financial Guarantee [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		991	801
Salvage and Subrogation Recoverable, net		132	142
(in millions)		859	659
Other [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		0	0
Salvage and Subrogation Recoverable, net		5	13
(in millions)		(5)	(13)
United States [Member] | Public Finance [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		525	243
Salvage and Subrogation Recoverable, net		11	8
(in millions)		514	235
United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		256	290
Salvage and Subrogation Recoverable, net		121	126
(in millions)		135	164
Non United States [Member] | Public Finance [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		30	30
Salvage and Subrogation Recoverable, net		0	0
(in millions)		30	30
First Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		239	283
Salvage and Subrogation Recoverable, net		56	48
(in millions)		183	235
Second Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		17	7
Salvage and Subrogation Recoverable, net		65	78
(in millions)		(48)	(71)
Prime [Member] | First Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		2	2
Salvage and Subrogation Recoverable, net		0	0
(in millions)		2	2
Alt-A [Member] | First Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		43	87
Salvage and Subrogation Recoverable, net		0	0
(in millions)		43	87
Option ARM [Member] | First Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		18	28
Salvage and Subrogation Recoverable, net		34	40
(in millions)		(16)	(12)
Subprime [Member] | First Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		176	166
Salvage and Subrogation Recoverable, net		22	8
(in millions)		154	158
Closed-end [Member] | Second Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		4	4
Salvage and Subrogation Recoverable, net		35	39
(in millions)		(31)	(35)
HELOCs [Member] | Second Lien [Member] | United States [Member] | RMBS [Member] | Financial Guarantee Insurance And Other 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 Reserve, net		13	3
Salvage and Subrogation Recoverable, net		30	39
(in millions)		$ (17)	$ (36)

[1] See “Components of Net Reserves (Salvage)” table for loss and LAE reserve and salvage and subrogation recoverable components.