Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 329,864	[1]	$ 358,571	[2]
Triple-X Life Insurance Transaction [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	2,189		2,750
Trust Preferred Securities (TruPS) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	3,255		4,379
Student Loan [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,645		1,818
Other structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	16,451		21,114
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	14,790		15,183
BIG [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	216		216
BIG [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	563		806
BIG [Member] | Student Loan [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	110		163
BIG [Member] | Other structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	828		863
BIG [Member] | BIG 1 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	7,056	[3]	8,023
BIG [Member] | BIG 1 [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		0
BIG [Member] | BIG 1 [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	436		679
BIG [Member] | BIG 1 [Member] | Student Loan [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		12
BIG [Member] | BIG 1 [Member] | Other structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	537		672
BIG [Member] | BIG 2 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	4,569		4,129
BIG [Member] | BIG 2 [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		0
BIG [Member] | BIG 2 [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	127		127
BIG [Member] | BIG 2 [Member] | Student Loan [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	68		68
BIG [Member] | BIG 2 [Member] | Other structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	254		151
BIG [Member] | BIG 3 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	3,165	[3]	3,031
BIG [Member] | BIG 3 [Member] | Triple-X Life Insurance Transaction [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	216		216
BIG [Member] | BIG 3 [Member] | Trust Preferred Securities (TruPS) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		0
BIG [Member] | BIG 3 [Member] | Student Loan [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	42		83
BIG [Member] | BIG 3 [Member] | Other structured finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	37		40
United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	272,114	[1],[4]	291,866	[2]
United States [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	6,082		7,067
United States [Member] | BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	8,268	[4]	7,784
United States [Member] | BIG [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	3,427		3,973
United States [Member] | BIG [Member] | BIG 1 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	4,902	[4]	4,765
United States [Member] | BIG [Member] | BIG 1 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	318		1,020
United States [Member] | BIG [Member] | BIG 2 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	3,191	[4]	2,883
United States [Member] | BIG [Member] | BIG 2 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	414		397
United States [Member] | BIG [Member] | BIG 3 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	175	[4]	136
United States [Member] | BIG [Member] | BIG 3 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	2,695		2,556
Non United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	28,128	[1]	29,577	[2]
Non United States [Member] | BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,378		1,378
Non United States [Member] | BIG [Member] | BIG 1 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	863		875
Non United States [Member] | BIG [Member] | BIG 2 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	515		503
Non United States [Member] | BIG [Member] | BIG 3 [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		0
First Lien [Member] | United States [Member] | Prime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	237		445
First Lien [Member] | United States [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,090		1,353
First Lien [Member] | United States [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	186		252
First Lien [Member] | United States [Member] | Subprime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	3,193		3,457
First Lien [Member] | United States [Member] | BIG [Member] | Prime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	124		284
First Lien [Member] | United States [Member] | BIG [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	621		793
First Lien [Member] | United States [Member] | BIG [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	96		141
First Lien [Member] | United States [Member] | BIG [Member] | Subprime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,220		1,304
First Lien [Member] | United States [Member] | BIG [Member] | BIG 1 [Member] | Prime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	21		225
First Lien [Member] | United States [Member] | BIG [Member] | BIG 1 [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	120		119
First Lien [Member] | United States [Member] | BIG [Member] | BIG 1 [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	27		39
First Lien [Member] | United States [Member] | BIG [Member] | BIG 1 [Member] | Subprime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	128		146
First Lien [Member] | United States [Member] | BIG [Member] | BIG 2 [Member] | Prime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	83		34
First Lien [Member] | United States [Member] | BIG [Member] | BIG 2 [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	42		73
First Lien [Member] | United States [Member] | BIG [Member] | BIG 2 [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	6		12
First Lien [Member] | United States [Member] | BIG [Member] | BIG 2 [Member] | Subprime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	210		228
First Lien [Member] | United States [Member] | BIG [Member] | BIG 3 [Member] | Prime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	20		25
First Lien [Member] | United States [Member] | BIG [Member] | BIG 3 [Member] | Alt-A [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	459		601
First Lien [Member] | United States [Member] | BIG [Member] | BIG 3 [Member] | Option ARM [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	63		90
First Lien [Member] | United States [Member] | BIG [Member] | BIG 3 [Member] | Subprime [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	882		930
Second Lien [Member] | United States [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,376		1,560
Second Lien [Member] | United States [Member] | BIG [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	1,366		1,451
Second Lien [Member] | United States [Member] | BIG [Member] | BIG 1 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	22		491
Second Lien [Member] | United States [Member] | BIG [Member] | BIG 2 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	73		50
Second Lien [Member] | United States [Member] | BIG [Member] | BIG 3 [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,271		$ 910

[1] Excludes $1.4 billion of loss mitigation securities insured and held by the Company as of June 30, 2016, which are primarily BIG.

[2] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of December 31, 2015, which are primarily BIG.

[3] Subsequent to June 30, 2016, and as a result of its July 1, 2016 Puerto Rico claim payments, the Company downgraded from BIG 1 to BIG 3 $1,803 million net par outstanding of financial guaranty insurance across two risks.

[4] Subsequent to June 30, 2016, and as a result of its July 1, 2016 Puerto Rico claim payments, the Company downgraded from BIG 1 to BIG 3 $1,803 million net par outstanding of financial guaranty insurance across two risks..