Outstanding Exposure - Geographic Distribution of Net Par Outstanding (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 risk		Dec. 31, 2013
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	13,161
Net par amount outstanding	$ 403,729	[1]	$ 459,107	[2]
Percent of Total Net Par Outstanding	100.00%
United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	12,904
Net par amount outstanding	363,294
Percent of Total Net Par Outstanding	90.10%
Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	257
Net par amount outstanding	40,435
Percent of Total Net Par Outstanding	9.90%
United Kingdom [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	114
Net par amount outstanding	19,856
Percent of Total Net Par Outstanding	4.90%
Australia [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	26
Net par amount outstanding	4,121
Percent of Total Net Par Outstanding	1.00%
Canada [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	10
Net par amount outstanding	3,526
Percent of Total Net Par Outstanding	0.90%
France [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	20
Net par amount outstanding	2,820
Percent of Total Net Par Outstanding	0.70%
Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	9
Net par amount outstanding	1,501
Percent of Total Net Par Outstanding	0.40%
Other Countries [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	78
Net par amount outstanding	8,611
Percent of Total Net Par Outstanding	2.00%
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	353,482		386,179
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	12,065
Net par amount outstanding	322,123	[1]	352,181	[2]
Percent of Total Net Par Outstanding	79.90%
Public Finance [Member] | California [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	1,465
Net par amount outstanding	50,668
Percent of Total Net Par Outstanding	12.60%
Public Finance [Member] | Pennsylvania [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	1,009
Net par amount outstanding	26,173
Percent of Total Net Par Outstanding	6.50%
Public Finance [Member] | New York [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	995
Net par amount outstanding	26,044
Percent of Total Net Par Outstanding	6.50%
Public Finance [Member] | Texas [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	1,239
Net par amount outstanding	25,449
Percent of Total Net Par Outstanding	6.30%
Public Finance [Member] | Illinois [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	830
Net par amount outstanding	22,825
Percent of Total Net Par Outstanding	5.70%
Public Finance [Member] | Florida [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	384
Net par amount outstanding	19,470
Percent of Total Net Par Outstanding	4.80%
Public Finance [Member] | New Jersey [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	602
Net par amount outstanding	13,558
Percent of Total Net Par Outstanding	3.40%
Public Finance [Member] | Michigan [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	668
Net par amount outstanding	12,739
Percent of Total Net Par Outstanding	3.20%
Public Finance [Member] | Georgia [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	192
Net par amount outstanding	8,217
Percent of Total Net Par Outstanding	2.00%
Public Finance [Member] | Ohio [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	507
Net par amount outstanding	7,818
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	4,174
Net par amount outstanding	109,162
Percent of Total Net Par Outstanding	27.00%
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	31,359	[1]	33,998	[2]
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	50,247		72,928
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Number of Risks	839
Net par amount outstanding	41,171	[1]	58,907	[2]
Percent of Total Net Par Outstanding	10.20%
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 9,076	[1]	$ 14,021	[2]

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

[2] Excludes $1.2 billion of loss mitigation securities insured and held by the Company as of December 31, 2013, which are primarily in the BIG category.