Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Net	$ 232,812	$ 236,392
% of total net par outstanding	100.00%	100.00%
AAA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,557	$ 3,788
% of total net par outstanding	1.50%	1.60%
AA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 25,279	$ 25,359
% of total net par outstanding	10.90%	10.70%
A
Schedule of Insured Financial Obligations [Line Items]
Net	$ 107,560	$ 106,091
% of total net par outstanding	46.20%	44.90%
BBB
Schedule of Insured Financial Obligations [Line Items]
Net	$ 91,030	$ 93,798
% of total net par outstanding	39.10%	39.70%
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 5,386	$ 7,356
% of total net par outstanding	2.30%	3.10%
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 224,095	$ 227,164
Public finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 179,648	$ 177,219
% of total net par outstanding	100.00%	100.00%
Public finance | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 44,447	$ 49,945
% of total net par outstanding	100.00%	100.00%
Public finance | AAA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 260	$ 272
% of total net par outstanding	0.10%	0.20%
Public finance | AAA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 2,016	$ 2,217
% of total net par outstanding	4.40%	4.50%
Public finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 17,042	$ 16,372
% of total net par outstanding	9.50%	9.20%
Public finance | AA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,671	$ 4,205
% of total net par outstanding	8.30%	8.40%
Public finance | A | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 96,931	$ 94,459
% of total net par outstanding	54.00%	53.30%
Public finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 9,633	$ 10,659
% of total net par outstanding	21.70%	21.30%
Public finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 61,845	$ 60,744
% of total net par outstanding	34.40%	34.30%
Public finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 28,606	$ 32,264
% of total net par outstanding	64.40%	64.60%
Public finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 4,091	$ 5,972
Public finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,570	$ 5,372
% of total net par outstanding	2.00%	3.00%
Public finance | BIG | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 521	$ 600
% of total net par outstanding	1.20%	1.20%
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 8,717	$ 9,228
Structured finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 7,935	$ 8,374
% of total net par outstanding	100.00%	100.00%
Structured finance | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 782	$ 854
% of total net par outstanding	100.00%	100.00%
Structured finance | AAA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 824	$ 806
% of total net par outstanding	10.40%	9.60%
Structured finance | AAA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 457	$ 493
% of total net par outstanding	58.50%	57.70%
Structured finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 4,554	$ 4,760
% of total net par outstanding	57.40%	56.80%
Structured finance | AA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 12	$ 22
% of total net par outstanding	1.50%	2.60%
Structured finance | A | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 813	$ 813
% of total net par outstanding	10.20%	9.70%
Structured finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 183	$ 160
% of total net par outstanding	23.40%	18.70%
Structured finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 449	$ 611
% of total net par outstanding	5.70%	7.30%
Structured finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 130	$ 179
% of total net par outstanding	16.60%	21.00%
Structured finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,295	$ 1,384
Structured finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,295	$ 1,384
% of total net par outstanding	16.30%	16.60%
Structured finance | BIG | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 0	$ 0
% of total net par outstanding	0.00%	0.00%