Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions		Jun. 30, 2015		Dec. 31, 2014
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 390,384	[1],[2]	$ 403,729	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
Loss mitigation bonds		$ 1,200		$ 1,300
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 25,309	[2]	$ 30,143
% of total net par outstanding		6.50%	[2]	7.50%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 92,308	[2]	$ 101,965
% of total net par outstanding		23.60%	[2]	25.30%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 182,322	[2]	$ 186,875
% of total net par outstanding		46.70%	[2]	46.30%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 70,041	[2]	$ 66,499
% of total net par outstanding		17.90%	[2]	16.40%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 20,404	[2]	$ 18,247
% of total net par outstanding		5.30%	[2]	4.50%
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 312,182	[1],[2]	$ 322,123	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 32,319	[1],[2]	$ 31,359	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
Public Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 3,280	[2]	$ 4,082
% of total net par outstanding		1.10%	[2]	1.30%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 695	[2]	$ 615
% of total net par outstanding		2.10%	[2]	2.00%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 80,550	[2]	$ 90,464
% of total net par outstanding		25.80%	[2]	28.10%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 2,735	[2]	$ 2,785
% of total net par outstanding		8.50%	[2]	8.90%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 171,633	[2]	$ 176,298
% of total net par outstanding		55.00%	[2]	54.70%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 7,627	[2]	$ 7,192
% of total net par outstanding		23.60%	[2]	22.90%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 46,822	[2]	$ 43,429
% of total net par outstanding		15.00%	[2]	13.50%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 19,651	[2]	$ 19,363
% of total net par outstanding		60.80%	[2]	61.70%
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 9,897	[2]	$ 7,850
% of total net par outstanding		3.10%	[2]	2.40%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,611	[2]	$ 1,404
% of total net par outstanding		5.00%	[2]	4.50%
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 38,906	[1],[2]	$ 41,171	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 6,977	[1],[2]	$ 9,076	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
Structured Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 17,619	[2]	$ 20,037
% of total net par outstanding		45.30%	[2]	48.70%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 3,715	[2]	$ 5,409
% of total net par outstanding		53.20%	[2]	59.60%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 8,628	[2]	$ 8,213
% of total net par outstanding		22.20%	[2]	19.90%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 395	[2]	$ 503
% of total net par outstanding		5.70%	[2]	5.50%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 2,684	[2]	$ 2,940
% of total net par outstanding		6.90%	[2]	7.10%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 378	[2]	$ 445
% of total net par outstanding		5.40%	[2]	4.90%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,797	[2]	$ 1,795
% of total net par outstanding		4.60%	[2]	4.40%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,771	[2]	$ 1,912
% of total net par outstanding		25.40%	[2]	21.10%
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 8,178	[2]	$ 8,186
% of total net par outstanding		21.00%	[2]	19.90%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 718	[2]	$ 807
% of total net par outstanding		10.30%	[2]	8.90%
Radian [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[1],[2]	$ 13,100

[1] Excludes $1.2 billion of loss mitigation securities insured and held by the Company as of June 30, 2015, which are primarily in the BIG category.

[2] amounts include $13.1 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 in the BIG category.