Reserve for Property and Casualty Insurance Claims and Claims Expense - Claims and allocated claim adjustment expenses, net of reinsurance (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) claim	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Auto insurance - liability coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	$ 49,263
Prior year reserve reestimates	341
Prior year reserve reestimates	301
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	35,701
All outstanding liabilities before 2017, net of recoverables	1,393
Liabilities for claims and claim adjustment expenses, net of recoverables	14,955
Auto insurance - liability coverage | Accident Year 2017
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	9,392	$ 9,332	$ 9,286	$ 9,341	$ 9,424
Prior year reserve reestimates	60
IBNR reserves plus expected development on reported claims	$ 581
Cumulative number of reported claims | claim	2,519,909
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 8,811	8,241	7,386	6,058	3,554
Auto insurance - liability coverage | Accident Year 2018
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	9,862	9,825	9,786	9,817
Prior year reserve reestimates	37
IBNR reserves plus expected development on reported claims	$ 1,140
Cumulative number of reported claims | claim	2,499,583
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 8,722	7,801	6,417	3,672
Auto insurance - liability coverage | Accident Year 2019
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	10,750	10,503	10,557
Prior year reserve reestimates	247
IBNR reserves plus expected development on reported claims	$ 2,080
Cumulative number of reported claims | claim	2,632,610
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 8,670	7,096	3,985
Auto insurance - liability coverage | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,770	8,773
Prior year reserve reestimates	(3)
IBNR reserves plus expected development on reported claims	$ 2,901
Cumulative number of reported claims | claim	1,891,726
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,869	3,143
Auto insurance - liability coverage | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	10,489
IBNR reserves plus expected development on reported claims	$ 6,860
Cumulative number of reported claims | claim	2,150,167
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 3,629
Auto insurance - liability coverage | Prior year reserve reestimates for pre-2017 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(51)
Auto insurance - liability coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	29
Auto insurance - physical damage coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	30,135
Prior year reserve reestimates	(131)
Prior year reserve reestimates	(152)
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	29,707
All outstanding liabilities before 2017, net of recoverables	7
Liabilities for claims and claim adjustment expenses, net of recoverables	435
Auto insurance - physical damage coverage | Accident Year 2017
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,613	5,610	5,612	5,627	5,738
Prior year reserve reestimates	3
IBNR reserves plus expected development on reported claims	$ 4
Cumulative number of reported claims | claim	4,634,171
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,609	5,609	5,614	5,625	5,398
Auto insurance - physical damage coverage | Accident Year 2018
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,652	5,659	5,704	5,788
Prior year reserve reestimates	(7)
IBNR reserves plus expected development on reported claims	$ 5
Cumulative number of reported claims | claim	4,686,395
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,647	5,650	5,693	5,475
Auto insurance - physical damage coverage | Accident Year 2019
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,150	6,188	6,269
Prior year reserve reestimates	(38)
IBNR reserves plus expected development on reported claims	$ (2)
Cumulative number of reported claims | claim	4,860,355
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,152	6,158	5,959
Auto insurance - physical damage coverage | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,419	5,508
Prior year reserve reestimates	(89)
IBNR reserves plus expected development on reported claims	$ (8)
Cumulative number of reported claims | claim	4,008,243
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,427	5,140
Auto insurance - physical damage coverage | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	7,301
IBNR reserves plus expected development on reported claims	$ 429
Cumulative number of reported claims | claim	4,407,369
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,872
Auto insurance - physical damage coverage | Prior year reserve reestimates for pre-2017 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(5)
Auto insurance - physical damage coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(14)
Homeowners
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	26,850
Prior year reserve reestimates	(64)
Prior year reserve reestimates	(153)
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	24,391
All outstanding liabilities before 2017, net of recoverables	115
Liabilities for claims and claim adjustment expenses, net of recoverables	2,574
Homeowners | Accident Year 2017
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	4,816	4,805	5,037	5,036	4,929
Prior year reserve reestimates	11
IBNR reserves plus expected development on reported claims	$ 60
Cumulative number of reported claims | claim	977,319
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,756	4,734	4,835	4,634	$ 3,521
Homeowners | Accident Year 2018
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	4,829	4,958	5,262	5,155
Prior year reserve reestimates	(129)
IBNR reserves plus expected development on reported claims	$ 82
Cumulative number of reported claims | claim	898,425
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,747	4,759	4,883	$ 3,775
Homeowners | Accident Year 2019
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	4,931	4,924	4,864
Prior year reserve reestimates	7
IBNR reserves plus expected development on reported claims	$ 153
Cumulative number of reported claims | claim	868,577
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,778	4,587	$ 3,535
Homeowners | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,839	5,792
Prior year reserve reestimates	47
IBNR reserves plus expected development on reported claims	$ 280
Cumulative number of reported claims | claim	982,690
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,559	$ 4,266
Homeowners | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,435
IBNR reserves plus expected development on reported claims	$ 1,884
Cumulative number of reported claims | claim	908,890
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,551
Homeowners | Prior year reserve reestimates for pre-2017 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(13)
Homeowners | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(70)
Other | Auto insurance - liability coverage
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(18)
Other | Auto insurance - physical damage coverage
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(2)
Other | Homeowners
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	$ (6)