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, 2022 USD ($) claim	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Auto insurance - liability coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	$ 54,036
Prior year reserve reestimates	980
Prior year reserve reestimates	1,154
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	37,986
All outstanding liabilities before 2018, net of recoverables	1,332
Liabilities for claims and claim adjustment expenses, net of recoverables	17,382
Auto insurance - liability coverage | Accident Year 2018
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	9,928	$ 9,835	$ 9,798	$ 9,758	$ 9,788
Prior year reserve reestimates	93
IBNR reserves plus expected development on reported claims	$ 603
Cumulative number of reported claims | claim	2,500,972
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 9,325	8,703	7,785	6,404	3,663
Auto insurance - liability coverage | Accident Year 2019
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	10,905	10,716	10,471	10,526	0
Prior year reserve reestimates	189
IBNR reserves plus expected development on reported claims	$ 1,242
Cumulative number of reported claims | claim	2,637,152
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 9,663	8,651	7,080	3,974	0
Auto insurance - liability coverage | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,984	8,744	8,748	0	0
Prior year reserve reestimates	240
IBNR reserves plus expected development on reported claims	$ 1,813
Cumulative number of reported claims | claim	1,904,004
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,171	5,858	3,135	0	0
Auto insurance - liability coverage | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	10,823	10,365	0	0	0
Prior year reserve reestimates	458
IBNR reserves plus expected development on reported claims	$ 3,488
Cumulative number of reported claims | claim	2,291,873
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,335	3,601	0	0	0
Auto insurance - liability coverage | Accident Year 2022
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	13,396	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 8,904
Cumulative number of reported claims | claim	2,311,893
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,492	0	0	0	0
Auto insurance - liability coverage | Prior year reserve reestimates for pre-2018 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	152
Auto insurance - liability coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	18
Auto insurance - liability coverage | Other
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	4
Auto insurance - physical damage coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	33,879
Prior year reserve reestimates	26
Prior year reserve reestimates	31
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	32,850
All outstanding liabilities before 2018, net of recoverables	11
Liabilities for claims and claim adjustment expenses, net of recoverables	1,040
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	5,637	5,640	5,647	5,692	5,775
Prior year reserve reestimates	(3)
IBNR reserves plus expected development on reported claims	$ 0
Cumulative number of reported claims | claim	4,686,877
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,637	5,635	5,638	5,681	5,464
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	6,134	6,136	6,174	6,255	0
Prior year reserve reestimates	(2)
IBNR reserves plus expected development on reported claims	$ (1)
Cumulative number of reported claims | claim	4,861,875
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,135	6,138	6,144	5,947	0
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	5,381	5,407	5,495	0	0
Prior year reserve reestimates	(26)
IBNR reserves plus expected development on reported claims	$ (7)
Cumulative number of reported claims | claim	4,013,428
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,388	5,415	5,129	0	0
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	7,342	7,285	0	0	0
Prior year reserve reestimates	57
IBNR reserves plus expected development on reported claims	$ (23)
Cumulative number of reported claims | claim	4,587,385
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,365	6,860	0	0	0
Auto insurance - physical damage coverage | Accident Year 2022
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	9,385	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 1,060
Cumulative number of reported claims | claim	4,711,189
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 8,325	0	0	0	0
Auto insurance - physical damage coverage | Prior year reserve reestimates for pre-2018 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	0
Auto insurance - physical damage coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	3
Auto insurance - physical damage coverage | Other
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	2
Homeowners
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	28,940
Prior year reserve reestimates	267
Prior year reserve reestimates	194
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	25,567
All outstanding liabilities before 2018, net of recoverables	86
Liabilities for claims and claim adjustment expenses, net of recoverables	3,459
Homeowners | Accident Year 2018
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	4,852	4,818	4,947	5,251	5,145
Prior year reserve reestimates	34
IBNR reserves plus expected development on reported claims	$ 42
Cumulative number of reported claims | claim	898,857
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,810	4,736	4,749	4,873	3,768
Homeowners | Accident Year 2019
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	4,931	4,920	4,912	4,853	0
Prior year reserve reestimates	11
IBNR reserves plus expected development on reported claims	$ 85
Cumulative number of reported claims | claim	869,860
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 4,846	4,768	4,576	3,527	0
Homeowners | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,921	5,827	5,781	0	0
Prior year reserve reestimates	94
IBNR reserves plus expected development on reported claims	$ 137
Cumulative number of reported claims | claim	989,034
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,784	5,548	4,257	0	0
Homeowners | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,532	6,404	0	0	0
Prior year reserve reestimates	128
IBNR reserves plus expected development on reported claims	$ 385
Cumulative number of reported claims | claim	992,897
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,147	4,538	0	0	0
Homeowners | Accident Year 2022
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,704	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 2,724
Cumulative number of reported claims | claim	705,357
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 3,980	$ 0	$ 0	$ 0	$ 0
Homeowners | Prior year reserve reestimates for pre-2018 accident years
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	(72)
Homeowners | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	2
Homeowners | Other
Increase (decrease) in claims and claims expense
Prior year reserve reestimates	$ (3)