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Variable Interest Entities - Additional Information (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2025 USD ($) policy Entity	Jun. 30, 2025 Entity	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) policy Entity	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) policy Entity
Variable Interest Entity [Line Items]
Assets	$ 12,101,000,000			$ 12,101,000,000		$ 11,901,000,000
Number of policies monitored | policy	16,000			16,000
Number of policies monitored, not within the scope of ASC 810 | policy	14,000			14,000
Number of policies that contain provisions for consolidation | policy	52			52		50
Net fair value gains and losses on FG VIEs are expected to reverse to zero at maturity of the VIE debt	$ 816,000,000			$ 816,000,000
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Number of entities | Entity	23			23		23
Number of entities consolidated in the period | Entity		1
Maximum loss exposure	$ 0			$ 0
Fair value gains (losses) on FG VIEs	$ 3,000,000		$ (2,000,000)	$ 6,000,000	$ (4,000,000)
Consolidated Investment Vehicles | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total number of entities consolidated | Entity	1			1		1
Assets	$ 136,000,000			$ 136,000,000		$ 101,000,000

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