Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 358,571	[1],[2]	$ 403,729	[3]
% of total net par outstanding		100.00%	[1],[2]	100.00%	[3]
United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 323,636
Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		34,935
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 20,837		$ 30,143
% of total net par outstanding		5.80%		7.50%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 79,402		$ 101,965
% of total net par outstanding		22.10%		25.30%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 167,246		$ 186,875
% of total net par outstanding		46.70%		46.30%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 75,903		$ 66,499
% of total net par outstanding		21.20%		16.40%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 15,183		$ 18,247
% of total net par outstanding		4.20%		4.50%
Loss mitigation bonds	[3]	$ 1,500		$ 1,300
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		321,443		353,482
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 291,866	[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		$ 29,577	[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		$ 3,053		$ 4,082
% of total net par outstanding		1.10%		1.30%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 709		$ 615
% of total net par outstanding		2.40%		2.00%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 69,274		$ 90,464
% of total net par outstanding		23.70%		28.10%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 2,017		$ 2,785
% of total net par outstanding		6.80%		8.90%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 157,440		$ 176,298
% of total net par outstanding		53.90%		54.70%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 6,765		$ 7,192
% of total net par outstanding		22.90%		22.90%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 54,315		$ 43,429
% of total net par outstanding		18.60%		13.50%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 18,708		$ 19,363
% of total net par outstanding		63.20%		61.70%
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 7,784		$ 7,850
% of total net par outstanding		2.70%		2.40%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,378		$ 1,404
% of total net par outstanding		4.70%		4.50%
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 37,128		$ 50,247
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 31,770	[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		$ 5,358	[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		$ 14,366		$ 20,037
% of total net par outstanding		45.20%		48.70%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 2,709		$ 5,409
% of total net par outstanding		50.60%		59.60%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 7,934		$ 8,213
% of total net par outstanding		25.00%		19.90%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 177		$ 503
% of total net par outstanding		3.30%		5.50%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 2,486		$ 2,940
% of total net par outstanding		7.80%		7.10%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 555		$ 445
% of total net par outstanding		10.30%		4.90%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,515		$ 1,795
% of total net par outstanding		4.80%		4.40%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1,365		$ 1,912
% of total net par outstanding		25.50%		21.10%
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 5,469		$ 8,186
% of total net par outstanding		17.20%		19.90%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 552		$ 807
% of total net par outstanding		10.30%		8.90%
Radian [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 10,900

[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.