Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 42,878	$ 42,414
Gross Unrealized Gains	843	1,022
Gross Unrealized Losses	3,096	2,995
Allowance for Credit Losses	20	16	$ 2	$ 1
Estimated Fair Value	40,605	40,425
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities trading	0	0
Total fixed maturity securities trading	0	0
Debt securities, amortized cost	42,878	42,414
Total fixed maturity securities	40,605	40,425
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	25,221	25,020
Gross Unrealized Gains	485	597
Gross Unrealized Losses	1,374	1,345
Allowance for Credit Losses	3	4	1	0
Estimated Fair Value	24,329	24,268
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	25,237	25,132
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	7,726	7,713
Gross Unrealized Gains	318	382
Gross Unrealized Losses	756	703
Allowance for Credit Losses	0	0
Estimated Fair Value	7,288	7,392
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	7,288	7,392
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,563	3,411
Gross Unrealized Gains	10	16
Gross Unrealized Losses	483	425
Allowance for Credit Losses	0	0
Estimated Fair Value	3,090	3,002
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,838	1,862
Gross Unrealized Gains	8	7
Gross Unrealized Losses	193	230
Allowance for Credit Losses	8	8
Estimated Fair Value	1,645	1,631
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,586	3,515
Gross Unrealized Gains	19	13
Gross Unrealized Losses	251	256
Allowance for Credit Losses	9	4
Estimated Fair Value	3,345	3,268
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	8,987	8,788
Gross Unrealized Gains	37	36
Gross Unrealized Losses	927	911
Allowance for Credit Losses	17	12	$ 1	$ 1
Estimated Fair Value	8,080	7,901
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	8,080	7,901
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	181	152
Gross Unrealized Gains	0	1
Gross Unrealized Losses	2	2
Allowance for Credit Losses	0	0
Estimated Fair Value	179	151
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	763	741
Gross Unrealized Gains	3	6
Gross Unrealized Losses	37	34
Allowance for Credit Losses	0	0
Estimated Fair Value	$ 729	$ 713

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