Outstanding Insurance Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 231,959	$ 236,807
% of total net par outstanding	100.00%	100.00%
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 4,111	$ 4,361
% of total net par outstanding	1.80%	1.80%
AA [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 26,635	$ 29,037
% of total net par outstanding	11.40%	12.30%
A [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 104,295	$ 111,329
% of total net par outstanding	45.00%	47.00%
BBB [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 88,542	$ 83,574
% of total net par outstanding	38.20%	35.30%
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 8,376	$ 8,506
% of total net par outstanding	3.60%	3.60%
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 222,436	$ 226,746
Public Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 173,143	$ 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	$ 49,293	$ 51,259
% of total net par outstanding	100.00%	100.00%
Public Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 368	$ 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	$ 2,459	$ 2,541
% of total net par outstanding	5.00%	5.00%
Public Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 17,800	$ 19,847
% of total net par outstanding	10.30%	11.30%
Public Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 4,916	$ 5,142
% of total net par outstanding	10.00%	10.00%
Public Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 92,807	$ 94,488
% of total net par outstanding	53.60%	53.90%
Public Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 10,314	$ 15,627
% of total net par outstanding	20.90%	30.40%
Public Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 56,448	$ 55,000
% of total net par outstanding	32.60%	31.30%
Public Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 30,741	$ 27,051
% of total net par outstanding	62.30%	52.80%
Public Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 6,583	$ 6,669
Public Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 5,720	$ 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	$ 863	$ 898
% of total net par outstanding	1.80%	1.80%
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 9,523	$ 10,061
Structured Finance [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 8,822	$ 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	$ 701	$ 761
% of total net par outstanding	100.00%	100.00%
Structured Finance [Member] | AAA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,118	$ 1,258
% of total net par outstanding	12.70%	13.50%
Structured Finance [Member] | AAA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 166	$ 181
% of total net par outstanding	23.70%	23.80%
Structured Finance [Member] | AA [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 3,885	$ 4,010
% of total net par outstanding	44.00%	43.10%
Structured Finance [Member] | AA [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 34	$ 38
% of total net par outstanding	4.90%	5.00%
Structured Finance [Member] | A [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,002	$ 1,030
% of total net par outstanding	11.30%	11.10%
Structured Finance [Member] | A [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 172	$ 184
% of total net par outstanding	24.50%	24.20%
Structured Finance [Member] | BBB [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,065	$ 1,206
% of total net par outstanding	12.10%	13.00%
Structured Finance [Member] | BBB [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 288	$ 317
% of total net par outstanding	41.10%	41.60%
Structured Finance [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,793	$ 1,837
Structured Finance [Member] | BIG [Member] | United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 1,752	$ 1,796
% of total net par outstanding	19.90%	19.30%
Structured Finance [Member] | BIG [Member] | Non United States [Member]
Schedule of Insured Financial Obligations [Line Items]
Total net exposure	$ 41	$ 41
% of total net par outstanding	5.80%	5.40%