Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 87	$ (74)
Fixed-maturity securities, available-for-sale:
Purchases	(344)	(321)
Sales	216	359
Maturities and paydowns	188	165
Short-term investments with original maturities of over three months:
Purchases	(2)	0
Maturities and paydowns	0	4
Net sales (purchases) of short-term investments with original maturities of less than three months	67	8
Sales of fixed-maturity securities, trading	8	72
Maturities and paydowns of fixed-maturity securities, trading	3	0
Paydowns of financial guaranty variable interest entities’ assets	5	6
Purchases of and contributions to other invested assets	(13)	(56)
Sales of and return of capital from other invested assets	10	17
Other	(4)	(1)
Net cash flows provided by (used in) investing activities	134	253
Cash flows from financing activities:
Dividends paid	(19)	(19)
Repurchases of common shares	(120)	(129)
Net paydowns of financial guaranty variable interest entities’ liabilities	(4)	(148)
Payments related to tax withholding for share-based compensation	(28)	(29)
Other	1	1
Distributions to noncontrolling interests from consolidated investment vehicles	0	(3)
Net cash flows provided by (used in) financing activities	(170)	(327)
Effect of foreign exchange rate changes	3	(1)
Increase (decrease) in cash and cash equivalents and restricted cash	54	(149)
Cash and cash equivalents and restricted cash at beginning of period	128	286	$ 286
Cash and cash equivalents and restricted cash at end of period	182	137	128
Supplemental cash flow information
Income taxes paid (received)	(3)	0
Interest paid on long-term debt	21	22
Supplemental disclosure of non-cash activities:
Receipt of fixed-maturity securities, available-for-sale	5	0
Distributions from equity method investments	0	7
Reconciliation of cash and cash equivalents and restricted cash to the condensed consolidated balance sheets:
Cash	177	115	121
Cash and cash equivalents of consolidated investment vehicles (See Note 8)	1	22
Restricted cash (included in other assets)	4	0
Cash and cash equivalents and restricted cash at end of period	$ 182	$ 137	$ 128