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, 2024	Dec. 31, 2023	Dec. 31, 2022
Increase (decrease) in claims and claims expense
Prior years	$ (308)	$ 549	$ 1,741
Auto
Increase (decrease) in claims and claims expense
Prior years	(364)	244	1,185
Homeowners
Increase (decrease) in claims and claims expense
Prior years	(395)	102	200
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	217	19	(32)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	166	84	272
Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	12	(6)
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	68	89	125
Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	(1)	(3)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	(370)	(24)	18
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(36)	(50)	(64)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(322)	36	77
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(7)	(18)	2
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	(5)	8	(1)
Catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	0	4
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	62	573	1,723
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(328)	294	1,249
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(73)	66	123
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	224	37	(34)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	171	76	273
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	12	(10)
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	68	89	125
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	(1)	(3)
Annual Reserve Review | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 58	$ 80	$ 118