Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ (74)	$ 312
Fixed-maturity securities, available-for-sale:
Purchases	(321)	(225)
Sales	359	455
Maturities and paydowns	165	129
Short-term investments with original maturities of over three months:
Purchases	0	(12)
Sales	0	3
Maturities and paydowns	4	15
Net sales (purchases) of short-term investments with original maturities of less than three months	8	(460)
Sales of fixed-maturity securities, trading	72	0
Paydowns of financial guaranty variable interest entities’ assets	6	7
Purchases of and contributions to other invested assets	(56)	(10)
Sales of and return of capital from other invested assets	17	5
Other	(1)	(1)
Net cash flows provided by (used in) investing activities	253	(94)
Cash flows from financing activities:
Dividends paid	(19)	(18)
Repurchases of common shares	(129)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(148)	(9)
Other	(28)	(15)
Cash flows from consolidated investment vehicles:
Repayment of warehouse financing debt	0	(152)
Borrowing (payment) under credit facilities	0	(30)
Distributions to noncontrolling interests from consolidated investment vehicles	(3)	(70)
Net cash flows provided by (used in) financing activities	(327)	(296)
Effect of foreign exchange rate changes	(1)	1
Increase (decrease) in cash and cash equivalents and restricted cash	(149)	(77)
Cash and cash equivalents and restricted cash at beginning of period	286	207	$ 207
Cash and cash equivalents and restricted cash at end of period	137	130	286
Supplemental cash flow information
Interest paid on long-term debt	22	10
Supplemental disclosure of non-cash activities:
Fixed-maturity securities, available-for-sale, received as salvage	0	1
Contributions from noncontrolling interests	0	3
Distributions to noncontrolling interests	0	3
Noncash, Distributions From Equity Method Investments	7	0
Reconciliation of cash and cash equivalents and restricted cash to the condensed consolidated balance sheets:
Cash	115	118	97
Cash and cash equivalents of consolidated investment vehicles (See Note 8)	22	(13)
Cash (included in assets held for sale)	0	25
Cash and cash equivalents and restricted cash at end of period	$ 137	$ 130	$ 286