Outstanding Exposure - Financial Guaranty Portfolio by Asset Class (Details) - USD ($) $ in Millions	Dec. 31, 2023	Aug. 31, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	$ 249,153	$ 108	$ 233,258
Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	239,296		224,099
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	9,857		9,159
U.S.
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	198,921
U.S. | Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	190,289		179,636
U.S. | Public finance | General obligation
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	74,609		71,868
U.S. | Public finance | Tax backed
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	33,060		33,752
U.S. | Public finance | Municipal utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	29,300		26,436
U.S. | Public finance | Transportation
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	22,052		19,688
U.S. | Public finance | Healthcare
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	12,604		11,304
U.S. | Public finance | Infrastructure finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	8,796		6,955
U.S. | Public finance | Higher education
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	7,250		7,137
U.S. | Public finance | Housing revenue
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,152		959
U.S. | Public finance | Investor-owned utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	329		332
U.S. | Public finance | Renewable energy
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	167		180
U.S. | Public finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	970		1,025
U.S. | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	8,632		8,228
U.S. | Structured finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	892		806
U.S. | Structured finance | Insurance securitizations
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	4,379		3,879
U.S. | Structured finance | RMBS
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,774		1,956
U.S. | Structured finance | Pooled corporate obligations
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	631		625
U.S. | Structured finance | Financial products
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	464		453
U.S. | Structured finance | Consumer receivables
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	314		437
U.S. | Structured finance | Subscription Finance Facilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	178		72
Non U.S.
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	50,232
Non U.S. | Public finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	49,007		44,463
Non U.S. | Public finance | Infrastructure finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	15,430		13,915
Non U.S. | Public finance | Renewable energy
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	2,030		2,086
Non U.S. | Public finance | Regulated utilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	20,545		17,855
Non U.S. | Public finance | Sovereign and sub-sovereign
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	9,869		9,526
Non U.S. | Public finance | Pooled infrastructure
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,133		1,081
Non U.S. | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	1,225		931
Non U.S. | Structured finance | Other
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	104		105
Non U.S. | Structured finance | RMBS
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	252		263
Non U.S. | Structured finance | Pooled corporate obligations
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	425		344
Non U.S. | Structured finance | Subscription Finance Facilities
Schedule of Insured Financial Obligations [Line Items]
Total net par outstanding	$ 444		$ 219