Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net income attributable to common shareholders	$ 20	$ (33)
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1)	(1)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	21	(33)
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation	1	0
Amortization of bond premium and discount	(3)	(3)
Share-based compensation	0	3
Unearned premiums, net	(6)	6
Losses and loss expenses, net	(4)	143
Ceded premiums payable	20	(1)
Premium receivables	(9)	(3)
Accrued interest payable	12	(37)
Amortization of Intangible Assets	12	7
Net investment gains (losses), including impairments	(1)	4
Variable interest entity activities	(3)	1
Other, net	(23)	(11)
Net Cash Provided by (Used in) Operating Activities, Total	18	77
Proceeds from Sale of Debt Securities, Available-for-Sale	30	63
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from matured bonds	42	6
Purchases of bonds	(72)	(104)
Proceeds from sales of other invested assets	7	41
Purchases of other invested assets	(82)	(14)
Change in short-term investments	71	146
Change in cash collateral	5	(16)
Proceeds from paydowns of consolidated VIE assets	43	57
Other, net	0	8
Net cash provided by investing activities	51	441
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax payments related to shares withheld for share-based compensation plans	(1)	(5)
Proceeds from (Payments to) Noncontrolling Interests	(1)	0
Payments of consolidated VIE liabilities, net	(46)	(174)
Net cash used in financing activities	(47)	(276)
Effect of foreign exchange on cash, cash equivalents and restricted cash	0	0
Net cash flow	21	243
Cash, cash equivalents, and restricted cash at beginning of period	274	61
Cash, cash equivalents, and restricted cash at end of period	296	304
Change in cash collateral	5	(16)
Tier 2 Notes
Net Cash Provided by (Used in) Financing Activities [Abstract]
Repayments of Secured Debt	0	(97)
Repayments of Secured Debt	0	97
Variable Interest Entity, Primary Beneficiary [Member]
Net Cash Provided by (Used in) Investing Activities [Abstract]
Change in cash collateral	6	254
Change in cash collateral	$ 6	$ 254