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		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Increase (decrease) in claims and claims expense
Prior years	$ 866	$ 161	$ 1,470	$ (65)
Auto
Increase (decrease) in claims and claims expense
Prior years	632	72	1,011	3
Homeowners
Increase (decrease) in claims and claims expense
Prior years	55	17	177	(156)
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(5)	(66)	(14)	(83)
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	64	25	175	58
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	120	113	124	115
Unfavorable reestimates			118	111
Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	(3)	(2)
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	875	162	1,441	142
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	643	77	1,069	31
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	51	14	95	12
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(2)	(66)	(18)	(69)
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	63	24	174	55
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	120	113	124	115
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	(3)	(2)
Catastrophe
Increase (decrease) in claims and claims expense
Prior years	(9)	(1)	29	(207)
Catastrophe | Nationwide Aggregate Reinsurance Program
Increase (decrease) in claims and claims expense
Prior years		40		240
Catastrophe | Auto
Increase (decrease) in claims and claims expense
Prior years	(11)	(5)	(58)	(28)
Catastrophe | Homeowners
Increase (decrease) in claims and claims expense
Prior years	4	3	82	(168)
Catastrophe | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(3)	0	4	(14)
Catastrophe | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	1	1	1	3
Catastrophe | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	0	0	0	0
Catastrophe | Protection Services
Increase (decrease) in claims and claims expense
Prior years	$ 0	$ 0	$ 0	0
Fire | Southern California Edison
Increase (decrease) in claims and claims expense
Prior years				$ 110