Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fixed maturity securities:
Fixed maturity securities	$ 43,702	$ 41,111
Equity securities:
Equity securities	726	659
Short-term and other	2,069	1,922
Total assets	46,497	43,692
Total liabilities	0	0
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	26,422	25,841
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	8,376	6,804
Asset-backed
Fixed maturity securities:
Fixed maturity securities	8,904	8,466
Common Stock
Equity securities:
Equity securities	197	180
Non-redeemable preferred stock
Equity securities:
Equity securities	529	479
Level 1
Fixed maturity securities:
Fixed maturity securities	227	223
Equity securities:
Equity securities	223	198
Short-term and other	2,017	1,852
Total assets	2,467	2,273
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	227	223
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	187	162
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	36	36
Level 2
Fixed maturity securities:
Fixed maturity securities	41,072	38,692
Equity securities:
Equity securities	493	441
Short-term and other	52	70
Total assets	41,617	39,203
Total liabilities	0	0
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	24,795	24,340
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	8,332	6,762
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	7,945	7,590
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	493	441
Level 3
Fixed maturity securities:
Fixed maturity securities	2,403	2,196
Equity securities:
Equity securities	10	20
Short-term and other	0	0
Total assets	2,413	2,216
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities	1,400	1,278
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities	44	42
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities	959	876
Level 3 | Common Stock
Equity securities:
Equity securities	10	18
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 0	$ 2