Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fixed maturity securities:
Fixed maturity securities	$ 40,605	$ 40,425
Equity securities:
Equity securities	691	683
Short term and other	1,820	2,008
Total assets	43,116	43,116
Other liabilities	0	1
Total liabilities	0	1
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	25,237	25,132
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	7,288	7,392
Asset-backed
Fixed maturity securities:
Fixed maturity securities	8,080	7,901
Common Stock
Equity securities:
Equity securities	206	191
Non-redeemable preferred stock
Equity securities:
Equity securities	485	492
Level 1
Fixed maturity securities:
Fixed maturity securities	189	161
Equity securities:
Equity securities	241	219
Short term and other	1,801	1,976
Total assets	2,231	2,356
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	189	161
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	195	167
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	46	52
Level 2
Fixed maturity securities:
Fixed maturity securities	38,420	38,274
Equity securities:
Equity securities	439	440
Short term and other	19	32
Total assets	38,878	38,746
Other liabilities	0	1
Total liabilities	0	1
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	23,966	23,926
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	7,245	7,348
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	7,209	7,000
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	439	440
Level 3
Fixed maturity securities:
Fixed maturity securities	1,996	1,990
Equity securities:
Equity securities	11	24
Short term and other	0	0
Total assets	2,007	2,014
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	1,082	1,045
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	43	44
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	871	901
Level 3 | Common Stock
Equity securities:
Equity securities	11	24
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 0	$ 0