Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Prior Year Reserve Reestimates Included in Claims and Claims Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Increase (decrease) in claims and claims expense
Prior years	$ 549	$ 1,741	$ 122
Auto
Increase (decrease) in claims and claims expense
Prior years	244	1,185	149
Homeowners
Increase (decrease) in claims and claims expense
Prior years	102	200	(135)
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	19	(32)	(107)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	84	272	119
Other business lines
Increase (decrease) in claims and claims expense
Prior years	12	(6)	(18)
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	89	125	116
Protection Services
Increase (decrease) in claims and claims expense
Prior years	(1)	(3)	(2)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	(24)	18	(202)
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(50)	(64)	(29)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	36	77	(166)
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(18)	2	(11)
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	8	(1)	3
Catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	4	1
Catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	0	0	0
Catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	0
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	573	1,723	324
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	294	1,249	178
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	66	123	31
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	37	(34)	(96)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	76	273	116
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	12	(10)	(19)
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	89	125	116
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	(1)	(3)	(2)
Annual Reserve Review | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 80	$ 118	$ 111