Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Jun. 30, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 329,864	[1]	$ 358,571	[2]
% of total net par outstanding	100.00%	[1]	100.00%	[2]
Loss mitigation bonds	$ 1,400		$ 1,500
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 16,061		$ 20,837
% of total net par outstanding	4.90%		5.80%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 67,953		$ 79,402
% of total net par outstanding	20.60%		22.10%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 150,933		$ 167,246
% of total net par outstanding	45.70%		46.70%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 80,127		$ 75,903
% of total net par outstanding	24.30%		21.20%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 14,790		$ 15,183
% of total net par outstanding	4.50%		4.20%
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 272,114	[1],[3]	$ 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	$ 28,128	[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	$ 2,376		$ 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	$ 695		$ 709
% of total net par outstanding	2.50%		2.40%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 59,310		$ 69,274
% of total net par outstanding	21.80%		23.70%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,775		$ 2,017
% of total net par outstanding	6.30%		6.80%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 142,028		$ 157,440
% of total net par outstanding	52.20%		53.90%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 6,440		$ 6,765
% 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	$ 60,132		$ 54,315
% of total net par outstanding	22.10%		18.60%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 17,840		$ 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	$ 8,268	[3]	$ 7,784
% of total net par outstanding	3.00%		2.70%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,378		$ 1,378
% of total net par outstanding	4.90%		4.70%
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 25,562	[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	$ 4,060	[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	$ 11,362		$ 14,366
% of total net par outstanding	44.40%		45.20%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,628		$ 2,709
% of total net par outstanding	40.10%		50.60%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 6,719		$ 7,934
% of total net par outstanding	26.30%		25.00%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 149		$ 177
% of total net par outstanding	3.70%		3.30%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,008		$ 2,486
% of total net par outstanding	7.90%		7.80%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 457		$ 555
% of total net par outstanding	11.20%		10.30%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 920		$ 1,515
% of total net par outstanding	3.60%		4.80%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,235		$ 1,365
% of total net par outstanding	30.40%		25.50%
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 4,553		$ 5,469
% of total net par outstanding	17.80%		17.20%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 591		$ 552
% of total net par outstanding	14.60%		10.30%

[1] Excludes $1.4 billion of loss mitigation securities insured and held by the Company as of June 30, 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.

[3] Subsequent to June 30, 2016, and as a result of its July 1, 2016 Puerto Rico claim payments, the Company downgraded from BIG 1 to BIG 3 $1,803 million net par outstanding of financial guaranty insurance across two risks..