Outstanding Insurance Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 230,898	$ 236,807
% of total net par outstanding	100.00%	100.00%
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 4,186	$ 4,361
% of total net par outstanding	1.80%	1.80%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 27,746	$ 29,037
% of total net par outstanding	12.00%	12.30%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 108,612	$ 111,329
% of total net par outstanding	47.00%	47.00%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 82,116	$ 83,574
% of total net par outstanding	35.60%	35.30%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 8,238	$ 8,506
% of total net par outstanding	3.60%	3.60%
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 221,370	$ 226,746
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 172,795	$ 175,487
% of total net par outstanding	100.00%	100.00%
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 48,575
% of total net par outstanding	100.00%
Public Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 48,575	$ 51,259
% of total net par outstanding		100.00%
Public Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 375	$ 381
% of total net par outstanding	0.20%	0.20%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 2,453
% of total net par outstanding	5.10%
Public Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 2,541
% of total net par outstanding		5.00%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 19,037	$ 19,847
% of total net par outstanding	11.00%	11.30%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 4,921
% of total net par outstanding	10.10%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 5,142
% of total net par outstanding		10.00%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 92,788	$ 94,488
% of total net par outstanding	53.70%	53.90%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 14,621
% of total net par outstanding	30.10%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 15,627
% of total net par outstanding		30.40%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 54,965	$ 55,000
% of total net par outstanding	31.80%	31.30%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 25,743
% of total net par outstanding	53.00%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 27,051
% of total net par outstanding		52.80%
Public Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 6,467	$ 6,669
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 5,630	$ 5,771
% of total net par outstanding	3.30%	3.30%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 837
% of total net par outstanding	1.70%
Public Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 837	$ 898
% of total net par outstanding		1.80%
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	9,528	$ 10,061
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 8,806	$ 9,300
% of total net par outstanding	100.00%	100.00%
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 722
% of total net par outstanding	100.00%
Structured Finance [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 761
% of total net par outstanding		100.00%
Structured Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,182	$ 1,258
% of total net par outstanding	13.40%	13.50%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 176
% of total net par outstanding	24.40%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 181
% of total net par outstanding		23.80%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 3,753	$ 4,010
% of total net par outstanding	42.70%	43.10%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 35
% of total net par outstanding	4.80%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 38
% of total net par outstanding		5.00%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,031	$ 1,030
% of total net par outstanding	11.70%	11.10%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 172
% of total net par outstanding	23.80%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 184
% of total net par outstanding		24.20%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,110	$ 1,206
% of total net par outstanding	12.60%	13.00%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 298
% of total net par outstanding	41.30%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 317
% of total net par outstanding		41.60%
Structured Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,771	$ 1,837
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,730	$ 1,796
% of total net par outstanding	19.60%	19.30%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 41
% of total net par outstanding	5.70%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure		$ 41
% of total net par outstanding		5.40%