Supplementary Insurance Information - Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 309	$ 288	$ 267
Reserves for claims and unpaid losses and LAE	13,087	11,974	11,074
Unearned premiums	3,451	3,246	3,041
Net earned premiums	6,531	6,085	5,404
Net investment income	742	717	730
Claims, losses and settlement expenses	4,033	3,629	3,157
Amortization of deferred policy acquisition costs	720	641	580
Other operating expenses	2,001	1,647	1,480
Net written premiums	6,692	6,206	5,573
Property and casualty insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	309	288	267
Reserves for claims and unpaid losses and LAE	13,087	11,974	11,074
Unearned premiums	3,451	3,246	3,041
Net earned premiums	6,531	6,085	5,404
Net investment income	729	683	663
Claims, losses and settlement expenses	4,017	3,629	3,157
Amortization of deferred policy acquisition costs	720	641	580
Other operating expenses	1,235	1,091	967
Net written premiums	6,692	6,206	5,573
Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income	13	34	67
Claims, losses and settlement expenses	16
Other operating expenses	$ 766	$ 556	$ 513