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, 2022	Mar. 31, 2021
Increase (decrease) in claims and claims expense
Prior years	$ 145	$ (241)
Auto
Increase (decrease) in claims and claims expense
Prior years	142	(36)
Homeowners
Increase (decrease) in claims and claims expense
Prior years	(10)	(203)
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(7)	(18)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	19	15
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	1	1
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	158	2
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	151	(17)
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(3)	5
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(11)	0
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	20	13
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	1	1
Catastrophe
Increase (decrease) in claims and claims expense
Prior years	(13)	(243)
Catastrophe | Nationwide Aggregate Reinsurance Program
Increase (decrease) in claims and claims expense
Prior years		150
Catastrophe | Auto
Increase (decrease) in claims and claims expense
Prior years	(9)	(19)
Catastrophe | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(7)	(208)
Catastrophe | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	4	(18)
Catastrophe | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	(1)	2
Catastrophe | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 0	0
Fire | Southern California Edison
Increase (decrease) in claims and claims expense
Prior years		$ 110