Claim and Claim Adjustment Expense Reserves - Commercial Auto (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) Claim	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2016	$ 4,685	$ 4,096	$ 3,679
Total net liability for unpaid claim and claim adjustment expenses	20,617	19,263	18,163	$ 16,929
Commercial auto
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	4,515
IBNR	1,085
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	2,973
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	1,542
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2016	5
Liability for unallocated claim adjustment expenses for accident years presented	26
Total net liability for unpaid claim and claim adjustment expenses	1,573
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	74	107	33
Total net development for the accident years presented above	68	110	26
Total net development for accident years prior to 2016	3	(3)	4
Total unallocated claim adjustment expense development	3	0	3
Commercial auto | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	194	195	197	200	$ 195	$ 190	$ 186	$ 186	$ 186	$ 198
IBNR	$ 0
Cumulative number of claims | Claim	30,459
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 193	193	192	190	185	175	154	126	93	$ 52
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(1)	(2)	(3)	5	5	4	0	0	(12)
IBNR, Total	(4)
Commercial auto | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	237	241	241	239	232	221	200	198	199
IBNR	$ 0
Cumulative number of claims | Claim	30,948
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 237	235	232	225	203	178	150	107	$ 58
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(4)	0	2	7	11	21	2	(1)
IBNR, Total	38
Commercial auto | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	259	260	255	254	245	227	227	229
IBNR	$ 1
Cumulative number of claims | Claim	34,333
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 257	256	249	238	212	175	128	$ 66
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(1)	5	1	9	18	0	(2)
IBNR, Total	30
Commercial auto | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	323	327	325	323	289	266	257
IBNR	$ 0
Cumulative number of claims | Claim	37,281
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 319	312	295	257	203	147	$ 77
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(4)	2	2	34	23	9
IBNR, Total	66
Commercial auto | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	299	303	298	304	303	310
IBNR	$ 7
Cumulative number of claims | Claim	29,192
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 287	276	246	197	134	$ 71
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(4)	5	(6)	1	(7)
IBNR, Total	(11)
Commercial auto | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	377	393	390	388	397
IBNR	$ 16
Cumulative number of claims | Claim	33,063
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 347	305	240	168	$ 83
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	(16)	3	2	(9)
IBNR, Total	(20)
Commercial auto | Short-Duration Insurance Contract, Accident Year 2022
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	506	496	465	437
IBNR	$ 55
Cumulative number of claims | Claim	37,327
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 411	334	236	$ 112
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	10	31	28
IBNR, Total	69
Commercial auto | Short-Duration Insurance Contract, Accident Year 2023
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	635	620	554
IBNR	$ 120
Cumulative number of claims | Claim	42,921
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 414	270	$ 127
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	15	66
IBNR, Total	81
Commercial auto | Short-Duration Insurance Contract, Accident Year 2024
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	799	726
IBNR	$ 270
Cumulative number of claims | Claim	49,670
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 345	$ 153
Net Strengthening (Releases) of Prior Accident Year Reserves
Total	73
IBNR, Total	73
Commercial auto | Short-Duration Insurance Contract, Accident Year 2025
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses
Total	886
IBNR	$ 616
Cumulative number of claims | Claim	41,075
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses
Total	$ 163