Fair Value Measurement - Fair Value Level 3 Rollforward Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Financial Guaranty Variable Interest Entities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at start of period	$ (164)	$ (554)	$ (715)
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	12	2
Other comprehensive income (loss)	3	3
Issuances	0	0
Settlements	375	149
Deconsolidations		7
Fair value at end of period	164	554
Change in unrealized gains/(losses) related to financial instruments held	3	0
Consolidated investment vehicles
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at start of period		0	$ (4,154)
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)		(45)
Other comprehensive income (loss)		(13)
Issuances		0
Settlements		13
Deconsolidations		4,199
Fair value at end of period		0
Change in unrealized gains/(losses) related to financial instruments held		0
Other Comprehensive Income (Loss) | Financial Guaranty Variable Interest Entities
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held	3	3
Other Comprehensive Income (Loss) | Consolidated investment vehicles
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held		0
Credit Risk Contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value at beginning of period	(50)	(162)
Total pre-tax realized and unrealized gains (losses) recorded in:
Net income (loss)	24	114
Other comprehensive income (loss)	0	0
Issuances	2	(1)
Settlements	(1)	(1)
Deconsolidations		0
Fair value at end of period	(29)	(50)
Change in unrealized gains/(losses)included in earnings related to financial instruments	13	112
Fixed-maturity securities | Obligations of state and political subdivisions
Fair Value Level 3 Rollforward
Fair value at beginning of period	6	47
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	0	1
Other comprehensive income (loss)	4	(2)
Purchases	0	0
Sales	0	0
Settlements	0	(3)
Reclassifications	0
Deconsolidations	0	0
Transfers into Level 3	0	3
Transfers out of Level 3	0	(40)
Fair value at end of period	10	6
Fixed-maturity securities | RMBS
Fair Value Level 3 Rollforward
Fair value at beginning of period	154	179
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	14	13
Other comprehensive income (loss)	2	(8)
Purchases	0	0
Sales	0	0
Settlements	(25)	(30)
Reclassifications	0
Deconsolidations	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value at end of period	145	154
Fixed-maturity securities | Asset-backed securities
Fair Value Level 3 Rollforward
Fair value at beginning of period	803	794
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	48	32
Other comprehensive income (loss)	1	(8)
Purchases	63	23
Sales	0	(2)
Settlements	(149)	(36)
Reclassifications	245
Deconsolidations	0	0
Transfers into Level 3	20	0
Transfers out of Level 3	0	0
Fair value at end of period	1,031	803
Fixed-maturity securities | Fixed Maturities, Trading Securities
Fair Value Level 3 Rollforward
Fair value at beginning of period	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	0
Other comprehensive income (loss)	0
Purchases	0
Sales	0
Settlements	(3)
Reclassifications	8
Deconsolidations	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair value at end of period	5	0
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	0
Fixed-maturity securities | Other Comprehensive Income (Loss) | Obligations of state and political subdivisions
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	4	0
Fixed-maturity securities | Other Comprehensive Income (Loss) | RMBS
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	2	(7)
Fixed-maturity securities | Other Comprehensive Income (Loss) | Asset-backed securities
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	(2)	9
Financial Guaranty Variable Interest Entities
Fair Value Level 3 Rollforward
Fair value at beginning of period	174	204
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(3)	9
Other comprehensive income (loss)	(1)	0
Purchases	0	0
Sales	0	0
Settlements	(23)	(33)
Reclassifications	0
Deconsolidations	0	(7)
Transfers into Level 3	0	1
Transfers out of Level 3	0	0
Fair value at end of period	147	174
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	(7)	4
Financial Guaranty Variable Interest Entities | Other Comprehensive Income (Loss)
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	(1)
Consolidated investment vehicles | Assets of CIVs, equity securities
Fair Value Level 3 Rollforward
Fair value at beginning of period	80	297
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)		51
Other comprehensive income (loss)		0
Purchases		42
Sales		(91)
Settlements		0
Deconsolidations		(219)
Transfers into Level 3		0
Transfers out of Level 3		0
Fair value at end of period		80
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI		11
Consolidated investment vehicles | Corporate securities
Fair Value Level 3 Rollforward
Fair value at beginning of period	0	96
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)		(3)
Other comprehensive income (loss)		0
Purchases		6
Sales		(15)
Settlements		0
Deconsolidations		(84)
Transfers into Level 3		0
Transfers out of Level 3		0
Fair value at end of period		0
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI		0
Consolidated investment vehicles | Equity Securities
Fair Value Level 3 Rollforward
Fair value at beginning of period	80
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	29
Other comprehensive income (loss)	0
Purchases	0
Sales	(10)
Settlements	0
Reclassifications	0
Deconsolidations	(1)
Transfers into Level 3	3
Transfers out of Level 3	(2)
Fair value at end of period	99	80
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	29
Consolidated investment vehicles | Structured products
Fair Value Level 3 Rollforward
Fair value at beginning of period	189	46
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(16)	21
Other comprehensive income (loss)	0	0
Purchases	102	5
Sales	(28)	(48)
Settlements	0	0
Reclassifications	(253)
Deconsolidations	(2)	165
Transfers into Level 3	10	0
Transfers out of Level 3	(2)	0
Fair value at end of period	0	189
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	0	10
Other
Fair Value Level 3 Rollforward
Fair value at beginning of period	14	50
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(10)	(32)
Other comprehensive income (loss)	1	0
Purchases	0	0
Sales	0	0
Settlements	0	(4)
Reclassifications	0
Deconsolidations	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value at end of period	5	14
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	(10)	(32)
Other | Other Comprehensive Income (Loss)
Total pretax realized and unrealized gains/(losses) recorded in:
Change in unrealized gains/(losses) related to financial instruments held, Included in OCI	$ 1	$ 0