Reserve for Property and Casualty Insurance Claims and Claims Expense - Incurred and claims expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Increase (decrease) in claims and claims expense
Prior years	$ 122	$ (436)	$ (130)
Auto
Increase (decrease) in claims and claims expense
Prior years	149	(107)	(323)
Homeowners
Increase (decrease) in claims and claims expense
Prior years	(153)	(439)	65
Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(107)	(66)	8
Commercial lines
Increase (decrease) in claims and claims expense
Prior years	119	36	17
Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	116	141	105
Protection Services
Increase (decrease) in claims and claims expense
Prior years	(2)	(1)	(2)
Catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	(202)	(503)	48
Catastrophe losses | Nationwide Aggregate Reinsurance Program
Increase (decrease) in claims and claims expense
Prior years	240
Catastrophe losses | PG&E And Southern California Edison
Increase (decrease) in claims and claims expense
Prior years		495
Catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	(29)	(44)	(17)
Catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	(165)	(422)	66
Catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(11)	(39)	0
Catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	3	2	(1)
Catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	0	0	0
Catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	0	0	0
Fire | Southern California Edison
Increase (decrease) in claims and claims expense
Prior years	110
Non-catastrophe losses
Increase (decrease) in claims and claims expense
Prior years	324	67	(178)
Non-catastrophe losses | Auto
Increase (decrease) in claims and claims expense
Prior years	178	(63)	(306)
Non-catastrophe losses | Homeowners
Increase (decrease) in claims and claims expense
Prior years	12	(17)	(1)
Non-catastrophe losses | Other personal lines
Increase (decrease) in claims and claims expense
Prior years	(96)	(27)	8
Non-catastrophe losses | Commercial lines
Increase (decrease) in claims and claims expense
Prior years	116	34	18
Non-catastrophe losses | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	116	141	105
Non-catastrophe losses | Protection Services
Increase (decrease) in claims and claims expense
Prior years	(2)	$ (1)	$ (2)
Annual reserve review | Run-off Property-Liability
Increase (decrease) in claims and claims expense
Prior years	$ 111