Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net income attributable to common shareholders	$ 19	$ 347
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1)	(1)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	21	348
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation	1	1
Amortization of bond premium and discount	(10)	(8)
Share-based compensation	12	13
Unearned premiums, net	(46)	(47)
Losses and loss expenses, net	66	(328)
Ceded premiums payable	56	0
Premium receivables	(8)	57
Accrued interest payable	(13)	72
Amortization of Intangible Assets	21	34
Net investment gains (losses), including impairments	7	(31)
Variable interest entity activities	0	(14)
Derivative assets and liabilities	21	(62)
Other, net	(14)	83
Net Cash Provided by (Used in) Operating Activities, Total	112	59
Proceeds from Sale of Debt Securities, Available-for-Sale	113	454
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from matured bonds	58	83
Purchases of bonds	(291)	(273)
Proceeds from sales of other invested assets	189	142
Purchases of other invested assets	(62)	(99)
Change in short-term investments	125	(58)
Change in cash collateral	(29)	60
Proceeds from paydowns of consolidated VIE assets	161	126
Other, net	8	0
Net cash provided by (used in) investing activities	521	435
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax payments related to shares withheld for share-based compensation plans	(5)	(4)
Proceeds from (Payments to) Noncontrolling Interests	(1)	1
Payments of consolidated VIE liabilities	(285)	(404)
Net cash used in financing activities	(392)	(479)
Effect of foreign exchange on cash, cash equivalents and restricted cash	0	(1)
Net cash flow	241	14
Cash, cash equivalents, and restricted cash at beginning of period	61	23
Cash, cash equivalents, and restricted cash at end of period	302	38
Change in cash collateral	(29)	60
Net realized gains on extinguishment of debt	0	(57)
Payment for Debt Extinguishment or Debt Prepayment Cost	0	(58)
Treasury Stock, Value, Acquired, Cost Method	(5)	(14)
Payments to Acquire Businesses, Net of Cash Acquired	(7)
Tier 2 Notes
Net Cash Provided by (Used in) Financing Activities [Abstract]
Repayments of Secured Debt	(97)	0
Repayments of Secured Debt	97	0
Variable Interest Entity, Primary Beneficiary [Member]
Net Cash Provided by (Used in) Investing Activities [Abstract]
Change in cash collateral	254	0
Change in cash collateral	$ 254	$ 0