Shareholders' Equity - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 5,713
Other comprehensive income (loss) before reclassifications	(22)	$ 92
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	8	(2)
Income (loss) before income taxes	144	120
Tax (provision) benefit	(31)	(23)
Other comprehensive income (loss)	(28)	95
Ending balance	5,629
Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	8	(2)
Fair value gains (losses) on FG VIEs		(1)
Income (loss) before income taxes	7	(3)
Tax (provision) benefit	(1)	0
Total amount reclassified from AOCI, net of tax	6	(3)
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)
Total AOCI
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(359)	(515)
Less: Amounts reclassified from AOCI to:
Ending balance	(387)	(420)
No Credit Impairment
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(202)	(343)
Other comprehensive income (loss) before reclassifications	(31)	91
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	(29)	89
Ending balance	(231)	(254)
No Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(2)	3
Fair value gains (losses) on FG VIEs		0
Income (loss) before income taxes	(2)	3
Tax (provision) benefit	0	(1)
Total amount reclassified from AOCI, net of tax	(2)	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	(104)	(110)
Other comprehensive income (loss) before reclassifications	10	1
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	1	5
Ending balance	(103)	(105)
Credit Impairment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	10	(5)
Fair value gains (losses) on FG VIEs		0
Income (loss) before income taxes	10	(5)
Tax (provision) benefit	(1)	1
Total amount reclassified from AOCI, net of tax	9	(4)
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	(20)	(23)
Other comprehensive income (loss) before reclassifications	(2)	(2)
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	(1)	(1)
Ending balance	(21)	(24)
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
Fair value gains (losses) on FG VIEs		(1)
Income (loss) before income taxes	(1)	(1)
Tax (provision) benefit	0	0
Total amount reclassified from AOCI, net of tax	(1)	(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	(38)	(45)
Other comprehensive income (loss) before reclassifications	1	2
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	1	2
Ending balance	(37)	(43)
Cumulative Translation Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Fair value gains (losses) on FG VIEs		0
Income (loss) before income taxes	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	5	6
Other comprehensive income (loss) before reclassifications	0	0
Less: Amounts reclassified from AOCI to:
Other comprehensive income (loss)	0	0
Ending balance	5	6
Cash Flow  Hedge | Reclassification out of Accumulated Other Comprehensive Income
Less: Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Fair value gains (losses) on FG VIEs		0
Income (loss) before income taxes	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