Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Incurred Claims, Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Recoverables (Details) claim in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) claim	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Auto insurance - liability coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	$ 64,308
Prior year reserve reestimates	(205)
Total prior year reserve reestimates	(63)
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	44,526
All outstanding liabilities before 2020, net of recoverables	1,400
Liabilities for claims and claim adjustment expenses, net of recoverables	21,182
Auto insurance - liability coverage | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,840	$ 8,819	$ 8,808	$ 8,565	$ 8,667
Prior year reserve reestimates	21
IBNR reserves plus expected development on reported claims	$ 541
Cumulative number of reported claims (in thousands) | claim	2,075
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 8,299	7,867	7,049	5,750	3,078
Auto insurance - liability coverage | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	11,272	11,217	10,897	10,448	0
Prior year reserve reestimates	55
IBNR reserves plus expected development on reported claims	$ 1,180
Cumulative number of reported claims (in thousands) | claim	2,439
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 10,092	9,147	7,333	3,569	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	13,538	13,281	13,282	0	0
Prior year reserve reestimates	257
IBNR reserves plus expected development on reported claims	$ 2,465
Cumulative number of reported claims (in thousands) | claim	2,607
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 11,073	9,086	4,458	0	0
Auto insurance - liability coverage | Accident Year 2023
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	14,787	15,325	0	0	0
Prior year reserve reestimates	(538)
IBNR reserves plus expected development on reported claims	$ 4,927
Cumulative number of reported claims (in thousands) | claim	2,583
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 9,860	5,084	0	0	0
Auto insurance - liability coverage | Accident Year 2024
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	15,871	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 10,669
Cumulative number of reported claims (in thousands) | claim	2,316
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,202	0	0	0	0
Auto insurance - liability coverage | Prior year reserve reestimates for pre-2020 accident years
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	159
Auto insurance - liability coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	(27)
Auto insurance - liability coverage | Other
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	10
Auto insurance - physical damage coverage
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	39,199
Prior year reserve reestimates	(294)
Total prior year reserve reestimates	(301)
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	38,488
All outstanding liabilities before 2020, net of recoverables	10
Liabilities for claims and claim adjustment expenses, net of recoverables	721
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	5,328	5,327	5,332	5,359	5,434
Prior year reserve reestimates	1
IBNR reserves plus expected development on reported claims	$ 3
Cumulative number of reported claims (in thousands) | claim	4,042
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,325	5,327	5,335	5,361	5,079
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	7,221	7,216	7,254	7,226	0
Prior year reserve reestimates	5
IBNR reserves plus expected development on reported claims	$ 1
Cumulative number of reported claims (in thousands) | claim	4,633
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,220	7,241	7,297	6,794	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	9,037	8,996	9,308	0	0
Prior year reserve reestimates	41
IBNR reserves plus expected development on reported claims	$ (7)
Cumulative number of reported claims (in thousands) | claim	4,977
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 9,044	9,087	8,252	0	0
Auto insurance - physical damage coverage | Accident Year 2023
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	9,081	9,422	0	0	0
Prior year reserve reestimates	(341)
IBNR reserves plus expected development on reported claims	$ (5)
Cumulative number of reported claims (in thousands) | claim	4,799
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 9,086	8,482	0	0	0
Auto insurance - physical damage coverage | Accident Year 2024
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,532	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 719
Cumulative number of reported claims (in thousands) | claim	4,222
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,813	0	0	0	0
Auto insurance - physical damage coverage | Prior year reserve reestimates for pre-2020 accident years
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	(1)
Auto insurance - physical damage coverage | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	(5)
Auto insurance - physical damage coverage | Other
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	(1)
Homeowners
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	36,185
Prior year reserve reestimates	(437)
Total prior year reserve reestimates	(395)
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	32,051
All outstanding liabilities before 2020, net of recoverables	132
Liabilities for claims and claim adjustment expenses, net of recoverables	4,266
Homeowners | Accident Year 2020
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	5,948	5,929	5,882	5,792	5,685
Prior year reserve reestimates	19
IBNR reserves plus expected development on reported claims	$ 77
Cumulative number of reported claims (in thousands) | claim	992
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,871	5,826	5,734	5,492	4,209
Homeowners | Accident Year 2021
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,555	6,514	6,457	6,310	0
Prior year reserve reestimates	41
IBNR reserves plus expected development on reported claims	$ 154
Cumulative number of reported claims (in thousands) | claim	998
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,401	6,286	6,052	4,459	0
Homeowners | Accident Year 2022
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	6,476	6,503	6,551	0	0
Prior year reserve reestimates	(27)
IBNR reserves plus expected development on reported claims	$ 257
Cumulative number of reported claims (in thousands) | claim	794
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 6,219	5,950	3,902	0	0
Homeowners | Accident Year 2023
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,612	9,082	0	0	0
Prior year reserve reestimates	(470)
IBNR reserves plus expected development on reported claims	$ 795
Cumulative number of reported claims (in thousands) | claim	1,026
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 7,817	5,788	0	0	0
Homeowners | Accident Year 2024
Increase (decrease) in claims and claims expense
Incurred claims and allocated claim adjustment expenses, net of recoverables	8,594	0	0	0	0
IBNR reserves plus expected development on reported claims	$ 2,851
Cumulative number of reported claims (in thousands) | claim	993
Cumulative paid claims and allocated claims adjustment expenses, net of recoverables	$ 5,743	$ 0	$ 0	$ 0	$ 0
Homeowners | Prior year reserve reestimates for pre-2020 accident years
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	19
Homeowners | Prior year reserve reestimates for ULAE
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	22
Homeowners | Other
Increase (decrease) in claims and claims expense
Total prior year reserve reestimates	$ 1