Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fixed maturity securities:
Fixed maturity securities	$ 42,579	$ 40,425
Equity securities:
Equity securities	668	683
Short-term and other	1,721	2,008
Total assets	44,968	43,116
Other liabilities	0	1
Total liabilities	0	1
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	26,751	25,132
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	7,148	7,392
Asset-backed
Fixed maturity securities:
Fixed maturity securities	8,680	7,901
Common Stock
Equity securities:
Equity securities	183	191
Non-redeemable preferred stock
Equity securities:
Equity securities	485	492
Level 1
Fixed maturity securities:
Fixed maturity securities	225	161
Equity securities:
Equity securities	218	219
Short-term and other	1,691	1,976
Total assets	2,134	2,356
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	225	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	171	167
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	47	52
Level 2
Fixed maturity securities:
Fixed maturity securities	40,157	38,274
Equity securities:
Equity securities	436	440
Short-term and other	30	32
Total assets	40,623	38,746
Other liabilities	0	1
Total liabilities	0	1
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	25,289	23,926
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	7,103	7,348
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	7,765	7,000
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	436	440
Level 3
Fixed maturity securities:
Fixed maturity securities	2,197	1,990
Equity securities:
Equity securities	14	24
Short-term and other	0	0
Total assets	2,211	2,014
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	1,237	1,045
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	45	44
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	915	901
Level 3 | Common Stock
Equity securities:
Equity securities	12	24
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 2	$ 0