Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Prior Year Reserve Re-Estimates Included in Claims and Claims Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Increase (decrease) in claims and claims expense
Prior years	$ (203)	$ 212	$ (354)	$ 197
Auto
Increase (decrease) in claims and claims expense
Prior years	(180)	97	(254)	72
Homeowners
Increase (decrease) in claims and claims expense
Prior years	(191)	94	(380)	74
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	61	3	113	6
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	107	8	158	32
Other business lines
Increase (decrease) in claims and claims expense
Prior years	(1)	10	4	11
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	2	1	6	3
Protection Services
Increase (decrease) in claims and claims expense
Prior years	(1)	(1)	(1)	(1)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	(138)	31	(300)	(11)
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(9)	(19)	(16)	(47)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(128)	53	(277)	45
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	1	(5)	(2)	(12)
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	(2)	2	(5)	3
Catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	0	0	0
Catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	0	0	0	0
Catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	0	0
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	(65)	181	(54)	208
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(171)	116	(238)	119
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(63)	41	(103)	29
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	60	8	115	18
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	109	6	163	29
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	(1)	10	4	11
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	2	1	6	3
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	$ (1)	$ (1)	$ (1)	$ (1)