Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 298,243	$ 296,318
% of total net par outstanding	100.00%	100.00%
Loss mitigation bonds	$ 2,100	$ 2,100
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 11,769	$ 15,491
% of total net par outstanding	3.90%	5.20%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 48,240	$ 52,490
% of total net par outstanding	16.20%	17.70%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 146,885	$ 142,144
% of total net par outstanding	49.30%	48.00%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 78,121	$ 73,119
% of total net par outstanding	26.20%	24.70%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 13,228	$ 13,074
% of total net par outstanding	4.40%	4.40%
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 277,393	$ 271,179
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 238,050	$ 244,798
% of total net par outstanding	100.00%	100.00%
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 39,343	$ 26,381
% of total net par outstanding	100.00%	100.00%
Public Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,816	$ 2,066
% of total net par outstanding	0.80%	0.80%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,156	$ 2,221
% of total net par outstanding	5.50%	8.40%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 42,529	$ 46,420
% of total net par outstanding	17.90%	19.00%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 204	$ 170
% of total net par outstanding	0.50%	0.60%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 132,212	$ 133,829
% of total net par outstanding	55.50%	54.70%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 12,711	$ 6,270
% of total net par outstanding	32.30%	23.80%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 54,294	$ 55,103
% of total net par outstanding	22.80%	22.50%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 22,199	$ 16,378
% of total net par outstanding	56.40%	62.10%
Public Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 9,272	$ 8,722
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 7,199	$ 7,380
% of total net par outstanding	3.00%	3.00%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,073	$ 1,342
% of total net par outstanding	5.30%	5.10%
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 20,850	$ 25,139
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 18,446	$ 22,057
% of total net par outstanding	100.00%	100.00%
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 2,404	$ 3,082
% of total net par outstanding	100.00%	100.00%
Structured Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 6,765	$ 9,757
% of total net par outstanding	36.70%	44.20%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,032	$ 1,447
% of total net par outstanding	42.90%	47.00%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 5,408	$ 5,773
% of total net par outstanding	29.30%	26.20%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 99	$ 127
% of total net par outstanding	4.10%	4.10%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 1,698	$ 1,589
% of total net par outstanding	9.20%	7.20%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 264	$ 456
% of total net par outstanding	11.00%	14.80%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 868	$ 879
% of total net par outstanding	4.70%	4.00%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 760	$ 759
% of total net par outstanding	31.60%	24.60%
Structured Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 3,956	$ 4,352
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 3,707	$ 4,059
% of total net par outstanding	20.10%	18.40%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 249	$ 293
% of total net par outstanding	10.40%	9.50%
MBIA UK Insurance Limited [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 12,200