Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 43,989	$ 43,481
Gross Unrealized Gains	796	715
Gross Unrealized Losses	2,767	3,040
Allowance for Credit Losses	47	45	$ 20	$ 16
Estimated Fair Value	41,971	41,111
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities trading	2	0
Total fixed maturity securities trading	2	0
Debt securities, amortized cost	43,991	43,481
Total fixed maturity securities	41,973	41,111
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	26,388	25,839
Gross Unrealized Gains	502	423
Gross Unrealized Losses	1,149	1,305
Allowance for Credit Losses	15	13	3	4
Estimated Fair Value	25,726	24,944
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	26,616	25,841
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	7,246	7,396
Gross Unrealized Gains	227	243
Gross Unrealized Losses	829	835
Allowance for Credit Losses	0	0
Estimated Fair Value	6,644	6,804
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	6,644	6,804
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,844	3,725
Gross Unrealized Gains	20	7
Gross Unrealized Losses	426	488
Allowance for Credit Losses	0	0
Estimated Fair Value	3,438	3,244
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,788	1,830
Gross Unrealized Gains	14	11
Gross Unrealized Losses	119	142
Allowance for Credit Losses	18	18
Estimated Fair Value	1,665	1,681
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,816	3,770
Gross Unrealized Gains	24	24
Gross Unrealized Losses	216	239
Allowance for Credit Losses	14	14
Estimated Fair Value	3,610	3,541
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,448	9,325
Gross Unrealized Gains	58	42
Gross Unrealized Losses	761	869
Allowance for Credit Losses	32	32	$ 17	$ 12
Estimated Fair Value	8,713	8,466
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	8,713	8,466
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	219	220
Gross Unrealized Gains	1	1
Gross Unrealized Losses	2	1
Allowance for Credit Losses	0	0
Estimated Fair Value	218	220
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	688	701
Gross Unrealized Gains	8	6
Gross Unrealized Losses	26	30
Allowance for Credit Losses	0	0
Estimated Fair Value	$ 670	$ 677

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