Shareholders' Equity - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 5,553	$ 5,765
Other comprehensive income (loss) before reclassifications	57	(22)
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(16)	8
Total before tax	229	144
Tax (provision) benefit	(44)	(31)
Other comprehensive income (loss)	71	(28)
Ending balance	5,657	5,682
Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(16)	8
Total before tax	(16)	7
Tax (provision) benefit	2	(1)
Total amount reclassified from AOCI, net of tax	(14)	6
Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Consolidated Investment Vehicles
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		(1)
Total AOCI
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(385)	(359)
Less: Amounts reclassified from AOCI to:
Ending balance	(314)	(387)
No Credit Impairment
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(235)	(202)
Other comprehensive income (loss) before reclassifications	46	(31)
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	52	(29)
Ending balance	(183)	(231)
No Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(6)	(2)
Total before tax	(6)	(2)
Tax (provision) benefit	0	0
Total amount reclassified from AOCI, net of tax	(6)	(2)
No Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Variable Interest Entities
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		0
Credit Impairment
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(99)	(104)
Other comprehensive income (loss) before reclassifications	13	10
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	21	1
Ending balance	(78)	(103)
Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(10)	10
Total before tax	(10)	10
Tax (provision) benefit	2	(1)
Total amount reclassified from AOCI, net of tax	(8)	9
Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Variable Interest Entities
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		0
ISCR on FG VIEs’ Liabilities with Recourse
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(18)	(20)
Other comprehensive income (loss) before reclassifications	(1)	(2)
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	(1)	(1)
Ending balance	(19)	(21)
ISCR on FG VIEs’ Liabilities with Recourse | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Total before tax	0	(1)
Tax (provision) benefit	0	0
Total amount reclassified from AOCI, net of tax	0	(1)
ISCR on FG VIEs’ Liabilities with Recourse | Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Variable Interest Entities
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		(1)
Cumulative Translation Adjustment
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(37)	(38)
Other comprehensive income (loss) before reclassifications	(1)	1
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	(1)	1
Ending balance	(38)	(37)
Cumulative Translation Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Total before tax	0	0
Tax (provision) benefit	0	0
Total amount reclassified from AOCI, net of tax	0	0
Cumulative Translation Adjustment | Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Variable Interest Entities
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		0
Cash Flow  Hedge
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	4	5
Other comprehensive income (loss) before reclassifications	0	0
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	0	0
Ending balance	4	5
Cash Flow  Hedge | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Total before tax	0	0
Tax (provision) benefit	0	0
Total amount reclassified from AOCI, net of tax	$ 0	0
Cash Flow  Hedge | Reclassification out of Accumulated Other Comprehensive Income | Financial Guaranty Variable Interest Entities
Less: Amounts reclassified from AOCI to:
Fair value gains (losses) on FG VIEs		$ 0