Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Net	$ 227,071	$ 236,392
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	218,905	227,164
Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	6,160	6,837
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	8,166	9,228
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	5,785	7,356
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	4,649	5,972
BIG | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	107	119
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,136	1,384
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net	2,471	2,443
BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,454	2,321
BIG | BIG 1 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	1
BIG | BIG 1 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	17	122
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net	198	181
BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	124	116
BIG | BIG 2 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	35	41
BIG | BIG 2 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	74	65
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net	3,116	4,732
BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,071	3,535
BIG | BIG 3 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	72	77
BIG | BIG 3 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,045	1,197
United States | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	177,842	177,219
United States | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	2,006	2,391
United States | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	7,449	8,374
United States | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	4,187	5,372
United States | BIG | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	1,029	1,265
United States | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,136	1,384
United States | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,029	1,765
United States | BIG | BIG 1 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	17	121
United States | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	124	116
United States | BIG | BIG 2 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	39	24
United States | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,034	3,491
United States | BIG | BIG 3 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	973	1,120
Non-U.S. public finance | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	41,063	49,945
Non-U.S. public finance | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	717	854
Non-U.S. public finance | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	462	600
Non-U.S. public finance | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	425	556
Non-U.S. public finance | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 37	$ 44