Investments - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged, amortized costs	$ 947	$ 1,223
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	11	30	$ 14
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	378	428
Fixed maturities, Gross Unrealized Capital Gains	0	0
Fixed maturities, Gross Unrealized Capital Losses	38	50
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest	340	378
US Treasury and Government
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	29	29
Fixed maturities, Gross Unrealized Capital Gains	0	0
Fixed maturities, Gross Unrealized Capital Losses	1	2
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest	28	27
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	445	491
Fixed maturities, Gross Unrealized Capital Gains	0	0
Fixed maturities, Gross Unrealized Capital Losses	71	82
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest	374	409
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	6,469	6,095
Fixed maturities, Gross Unrealized Capital Gains	56	50
Fixed maturities, Gross Unrealized Capital Losses	841	896
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest	5,684	5,249
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	4,406	4,035
Fixed maturities, Gross Unrealized Capital Gains	42	31
Fixed maturities, Gross Unrealized Capital Losses	225	264
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	1	3
Debt Securities, Available-for-Sale, Excluding Accrued Interest	4,222	3,799
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	2,209	2,087
Fixed maturities, Gross Unrealized Capital Gains	20	17
Fixed maturities, Gross Unrealized Capital Losses	213	235
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	1	1	3
Debt Securities, Available-for-Sale, Excluding Accrued Interest	2,015	1,868
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	2,334	2,160
Fixed maturities, Gross Unrealized Capital Gains	22	15
Fixed maturities, Gross Unrealized Capital Losses	99	138
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	8	8	1
Debt Securities, Available-for-Sale, Excluding Accrued Interest	2,249	2,029
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	2,876	2,638
Fixed maturities, Gross Unrealized Capital Gains	23	19
Fixed maturities, Gross Unrealized Capital Losses	107	128
Embedded Derivatives	0	(4)
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest	2,792	2,525
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	2,449	2,459
Fixed maturities, Gross Unrealized Capital Gains	3	2
Fixed maturities, Gross Unrealized Capital Losses	290	333
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	17	$ 9
Debt Securities, Available-for-Sale, Excluding Accrued Interest	2,162	2,111
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	2,035	1,741
Fixed maturities, Gross Unrealized Capital Gains	18	24
Fixed maturities, Gross Unrealized Capital Losses	24	25
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	1	1
Debt Securities, Available-for-Sale, Excluding Accrued Interest	2,028	1,739
Embedded derivatives within fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	23,630	22,163
Total fixed maturities, less securities pledged, Amortized Cost	22,683	20,940
Fixed maturities, Gross Unrealized Capital Gains	184	158
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	184	158
Fixed maturities, Gross Unrealized Capital Losses	1,909	2,153
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	1,819	2,019
Embedded Derivatives	0	(4)
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	11	30
Debt Securities, Available-for-Sale, Excluding Accrued Interest	21,894	20,134
Total fixed maturities, less securities pledged, Fair Value	21,037	19,045
Embedded derivatives within fixed maturities | One America
Available-for-sale Securities Including Securities Pledged [Line Items]
Total fixed maturities, less securities pledged, Fair Value	1,400
Collateral Pledged
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged	857	1,089
Collateral Pledged | Embedded derivatives within fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged, amortized costs	947	1,223
Securities pledged, Gross Unrealized Capital Gains	0	0
Available-for-sale Securities, Pledged as Collateral, Debt Securities, Unrecognized Holding Loss	90	134
Embedded Derivatives	0	0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Securities pledged	$ 857	$ 1,089