Outstanding Exposure - Financial Guaranty Portfolio by Asset Class (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	$ 233,258	$ 236,392
Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	224,099	227,164
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	9,159	9,228
U.S.
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	187,864
U.S. | Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	179,636	177,219
U.S. | Public finance | General obligation
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	71,868	72,896
U.S. | Public finance | Tax backed
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	33,752	35,726
U.S. | Public finance | Municipal utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	26,436	25,556
U.S. | Public finance | Transportation
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	19,688	17,241
U.S. | Public finance | Healthcare
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	11,304	9,588
U.S. | Public finance | Higher education
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	7,137	6,927
U.S. | Public finance | Infrastructure finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	6,955	6,329
U.S. | Public finance | Housing revenue
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	959	1,000
U.S. | Public finance | Investor-owned utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	332	611
U.S. | Public finance | Renewable energy
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	180	193
U.S. | Public finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,025	1,152
U.S. | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	8,228	8,374
U.S. | Structured finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	878	665
U.S. | Structured finance | Life insurance transactions
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	3,879	3,431
U.S. | Structured finance | RMBS
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,956	2,391
U.S. | Structured finance | Pooled corporate obligations
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	625	534
U.S. | Structured finance | Financial products
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	453	770
U.S. | Structured finance | Consumer receivables
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	437	583
Non U.S.
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	45,394
Non U.S. | Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	44,463	49,945
Non U.S. | Public finance | Infrastructure finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	13,915	16,475
Non U.S. | Public finance | Renewable energy
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	2,086	2,398
Non U.S. | Public finance | Regulated utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	17,855	18,814
Non U.S. | Public finance | Sovereign and sub-sovereign
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	9,526	10,886
Non U.S. | Public finance | Pooled infrastructure
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,081	1,372
Non U.S. | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	931	854
Non U.S. | Structured finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	324	178
Non U.S. | Structured finance | RMBS
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	263	325
Non U.S. | Structured finance | Pooled corporate obligations
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	$ 344	$ 351