Outstanding Exposure - Geographic Distribution of Net Par Outstanding (Details) $ in Millions	Dec. 31, 2015 USD ($) risk		Dec. 31, 2014 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	12,567
Net Par Outstanding	$ 358,571	[1],[2]	$ 403,729	[3]
Percent of Total Net Par Outstanding	100.00%
United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	12,338
Net Par Outstanding	$ 323,636
Percent of Total Net Par Outstanding	90.20%
Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	229
Net Par Outstanding	$ 34,935
Percent of Total Net Par Outstanding	9.80%
United Kingdom [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	101
Net Par Outstanding	$ 17,565
Percent of Total Net Par Outstanding	4.90%
Australia [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	22
Net Par Outstanding	$ 3,349
Percent of Total Net Par Outstanding	0.90%
Canada [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	10
Net Par Outstanding	$ 3,099
Percent of Total Net Par Outstanding	0.90%
France [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	16
Net Par Outstanding	$ 2,609
Percent of Total Net Par Outstanding	0.70%
Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	8
Net Par Outstanding	$ 1,296
Percent of Total Net Par Outstanding	0.40%
Other Countries [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	72
Net Par Outstanding	$ 7,017
Percent of Total Net Par Outstanding	2.00%
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 321,443		353,482
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	11,615
Net Par Outstanding	$ 291,866	[1],[2]	322,123	[3]
Percent of Total Net Par Outstanding	81.30%
Public Finance [Member] | California [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	1,514
Net Par Outstanding	$ 47,731
Percent of Total Net Par Outstanding	13.30%
Public Finance [Member] | Pennsylvania [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	944
Net Par Outstanding	$ 23,655
Percent of Total Net Par Outstanding	6.60%
Public Finance [Member] | New York [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	961
Net Par Outstanding	$ 22,513
Percent of Total Net Par Outstanding	6.30%
Public Finance [Member] | Texas [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	1,307
Net Par Outstanding	$ 23,891
Percent of Total Net Par Outstanding	6.70%
Public Finance [Member] | Illinois [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	816
Net Par Outstanding	$ 22,220
Percent of Total Net Par Outstanding	6.20%
Public Finance [Member] | Florida [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	369
Net Par Outstanding	$ 16,595
Percent of Total Net Par Outstanding	4.60%
Public Finance [Member] | New Jersey [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	553
Net Par Outstanding	$ 13,605
Percent of Total Net Par Outstanding	3.80%
Public Finance [Member] | Michigan [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	577
Net Par Outstanding	$ 10,898
Percent of Total Net Par Outstanding	3.00%
Public Finance [Member] | Georgia [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	183
Net Par Outstanding	$ 6,991
Percent of Total Net Par Outstanding	1.90%
Public Finance [Member] | Ohio [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	464
Net Par Outstanding	$ 6,753
Percent of Total Net Par Outstanding	1.90%
Public Finance [Member] | Other States and U.S. Territories [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	3,927
Net Par Outstanding	$ 97,014
Percent of Total Net Par Outstanding	27.00%
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 29,577	[1],[2]	31,359	[3]
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 37,128		50,247
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks | risk	723
Net Par Outstanding	$ 31,770	[1],[2]	41,171	[3]
Percent of Total Net Par Outstanding	8.90%
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 5,358	[1],[2]	$ 9,076	[3]

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

[2] The December 31, 2015 amounts include $10.9 billion of net par acquired from Radian Asset.

[3] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily BIG.