Reserve for Property and Casualty Insurance Claims and Claims Expense - Prior year reserve reestimates included in claims and claims expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Increase (decrease) in claims and claims expense
Prior years	$ 212	$ 459	$ 197	$ 604
Auto
Increase (decrease) in claims and claims expense
Prior years	97	237	72	379
Homeowners
Increase (decrease) in claims and claims expense
Prior years	94	135	74	128
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	3	(2)	6	(9)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	8	92	32	111
Other business lines
Increase (decrease) in claims and claims expense
Prior years	10	(3)	11	(6)
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	1	3	3	4
Protection Services
Increase (decrease) in claims and claims expense
Prior years	(1)	(3)	(1)	(3)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	31	51	(11)	38
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(19)	(38)	(47)	(47)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	53	85	45	74
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(5)	3	(12)	7
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	2	1	3	0
Catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	0	0	4
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	181	408	208	566
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	116	275	119	426
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	41	50	29	54
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	8	(5)	18	(16)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	6	91	29	111
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	10	(3)	11	(10)
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	1	3	3	4
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	$ (1)	$ (3)	$ (1)	$ (3)