Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Mar. 31, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 347,015	[1]	$ 358,571	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Loss mitigation bonds	$ 1,500		$ 1,500
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 19,711		$ 20,837
% of total net par outstanding	5.70%		5.80%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 74,938		$ 79,402
% of total net par outstanding	21.60%		22.10%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 155,345		$ 167,246
% of total net par outstanding	44.70%		46.70%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 81,904		$ 75,903
% of total net par outstanding	23.60%		21.20%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 15,117		$ 15,183
% of total net par outstanding	4.40%		4.20%
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 282,055	[1]	$ 291,866	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 29,385	[1]	$ 29,577	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Public Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,541		$ 3,053
% of total net par outstanding	0.90%		1.10%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 688		$ 709
% of total net par outstanding	2.30%		2.40%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 65,310		$ 69,274
% of total net par outstanding	23.20%		23.70%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,969		$ 2,017
% of total net par outstanding	6.70%		6.80%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 145,515		$ 157,440
% of total net par outstanding	51.60%		53.90%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 6,695		$ 6,765
% of total net par outstanding	22.80%		22.90%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 60,736		$ 54,315
% of total net par outstanding	21.50%		18.60%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 18,622		$ 18,708
% of total net par outstanding	63.40%		63.20%
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 7,953		$ 7,784
% of total net par outstanding	2.80%		2.70%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,411		$ 1,378
% of total net par outstanding	4.80%		4.70%
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 30,452	[1]	$ 31,770	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 5,123	[1]	$ 5,358	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Structured Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 13,953		$ 14,366
% of total net par outstanding	45.80%		45.20%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,529		$ 2,709
% of total net par outstanding	49.40%		50.60%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 7,505		$ 7,934
% of total net par outstanding	24.70%		25.00%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 154		$ 177
% of total net par outstanding	3.00%		3.30%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,584		$ 2,486
% of total net par outstanding	8.50%		7.80%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 551		$ 555
% of total net par outstanding	10.80%		10.30%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,279		$ 1,515
% of total net par outstanding	4.20%		4.80%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,267		$ 1,365
% of total net par outstanding	24.70%		25.50%
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 5,131		$ 5,469
% of total net par outstanding	16.80%		17.20%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 622		$ 552
% of total net par outstanding	12.10%		10.30%

[1] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of March 31, 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.