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Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Variable Interest Entity [Line Items]
Assets	$ 12,095	$ 11,901
Liabilities	6,366	6,348
Cash	301	121	$ 92
FG VIEs’ assets	176	147
FG VIEs' liabilities	201	164
Contract with customer, asset	35
Variable Interest Entity, Primary Beneficiary \| Recourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	186	155
Variable Interest Entity, Primary Beneficiary \| Nonrecourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	16	9
Variable Interest Entity, Primary Beneficiary \| RMBS \| Nonrecourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	9	9
Variable Interest Entity, Primary Beneficiary \| Other (includes $32 at fair value in 2025) (1) (2) \| Recourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	34	0
Variable Interest Entity, Primary Beneficiary \| Other (includes $32 at fair value in 2025) (1) (2) \| Nonrecourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	7	0
FG VIEs' liabilities	6
Variable Interest Entity, Primary Beneficiary \| United States \| RMBS \| Recourse \| Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	152	155
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	211	147
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary \| Other (includes $32 at fair value in 2025) (1) (2)
Variable Interest Entity [Line Items]
Assets	67	0
FG VIEs’ assets	32
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary \| United States \| RMBS
Variable Interest Entity [Line Items]
Assets	$ 144	$ 147