Supplementary Insurance Information - Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 320	$ 309	$ 288
Reserves for claims and unpaid losses and LAE	14,179	13,087	11,974
Unearned premiums	3,584	3,451	3,246
Net earned premiums	7,036	6,531	6,085
Net investment income	780	742	717
Claims, losses and settlement expenses	4,460	4,033	3,629
Amortization of deferred policy acquisition costs	766	720	641
Other operating expenses	1,974	2,001	1,647
Net written premiums	7,139	6,692	6,206
Property and casualty insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	320	309	288
Reserves for claims and unpaid losses and LAE	14,179	13,087	11,974
Unearned premiums	3,584	3,451	3,246
Net earned premiums	7,036	6,531	6,085
Net investment income	784	729	683
Claims, losses and settlement expenses	4,455	4,017	3,629
Amortization of deferred policy acquisition costs	766	720	641
Other operating expenses	1,279	1,235	1,091
Net written premiums	7,139	6,692	6,206
Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income	(4)	13	34
Claims, losses and settlement expenses	5	16
Other operating expenses	$ 695	$ 766	$ 556