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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Increase (decrease) in claims and claims expense
Prior years	$ 183	$ 866	$ 380	$ 1,470
Auto
Increase (decrease) in claims and claims expense
Prior years	33	632	105	1,011
Homeowners
Increase (decrease) in claims and claims expense
Prior years	62	53	136	181
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(14)	(5)	(8)	(14)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	19	64	51	175
Other business lines
Increase (decrease) in claims and claims expense
Prior years	1	2	12	(4)
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	82	120	85	124
Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	(1)	(3)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	17	(9)	6	29
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	6	(11)	(41)	(58)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	16	3	61	77
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(11)	(3)	(23)	4
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	6	1	9	1
Catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	1	0	5
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	166	875	374	1,441
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	27	643	146	1,069
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	46	50	75	104
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(3)	(2)	15	(18)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	13	63	42	174
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	1	1	12	(9)
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	82	120	85	124
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	(1)	(3)
Annual Reserve Review | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 80	$ 118	$ 80	$ 118