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
	Mar. 31, 2023	Mar. 31, 2022
Increase (decrease) in claims and claims expense
Prior years	$ (15)	$ 145
Auto
Increase (decrease) in claims and claims expense
Prior years	(25)	142
Homeowners
Increase (decrease) in claims and claims expense
Prior years	(20)	(7)
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	3	(7)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	24	19
Other business lines
Increase (decrease) in claims and claims expense
Prior years	1	(3)
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	2	1
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	27	158
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	3	151
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(12)	4
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	10	(11)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	23	20
Non-catastrophe losses | Other business lines
Increase (decrease) in claims and claims expense
Prior years	1	(7)
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	2	1
Catastrophe
Increase (decrease) in claims and claims expense
Prior years	(42)	(13)
Catastrophe | Auto
Increase (decrease) in claims and claims expense
Prior years	(28)	(9)
Catastrophe | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(8)	(11)
Catastrophe | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(7)	4
Catastrophe | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	1	(1)
Catastrophe | Other business lines
Increase (decrease) in claims and claims expense
Prior years	0	4
Catastrophe | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 0	$ 0