Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - Commercial Auto (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 ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2013	$ 4,348	$ 3,830	$ 4,216
Total net liability for unpaid claim and claim adjustment expenses	19,908	19,205	18,701	$ 17,885
Property and casualty
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total net liability for unpaid claim and claim adjustment expenses	15,996	15,270
Commercial Auto
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	2,771
IBNR	521
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	2,004
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	767
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2013	4
Liability for unallocated claim adjustment expenses for accident years presented	16
Total net liability for unpaid claim and claim adjustment expenses	787
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	47	53	32
Total net development for accident years prior to 2013	2	0	1
Total unallocated claim adjustment expense development	0	0	0
Total	49	53	33
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	243	241	241	241	$ 245	$ 245	$ 249	$ 265	$ 265	$ 246
IBNR	$ 3
Cumulative number of claims | Claim	39,431
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 239	239	239	238	234	225	200	168	135	$ 74
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	2	0	0	(4)	0	(4)	(16)	0	19
IBNR, Total	(3)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2014
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	201	202	201	201	205	205	212	223	234
IBNR	$ 1
Cumulative number of claims | Claim	33,631
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 199	199	198	196	187	166	137	102	$ 64
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)	1	0	(4)	0	(7)	(11)	(11)
IBNR, Total	(33)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	182	183	181	183	190	190	199	201
IBNR	$ 3
Cumulative number of claims | Claim	30,430
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 179	178	175	172	153	130	96	$ 52
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)	2	(2)	(7)	0	(9)	(2)
IBNR, Total	(19)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	200	195	190	186	186	186	198
IBNR	$ 7
Cumulative number of claims | Claim	30,452
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 190	185	175	154	126	93	$ 52
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	5	5	4	0	0	(12)
IBNR, Total	2
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	239	232	221	200	198	199
IBNR	$ 3
Cumulative number of claims | Claim	30,947
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 225	203	178	150	107	$ 58
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	7	11	21	2	(1)
IBNR, Total	40
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	254	245	227	227	229
IBNR	$ 5
Cumulative number of claims | Claim	34,319
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 238	212	175	128	$ 66
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	9	18	0	(2)
IBNR, Total	25
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	323	289	266	257
IBNR	$ 27
Cumulative number of claims | Claim	37,237
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 257	203	147	$ 77
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	34	23	9
IBNR, Total	66
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	304	303	310
IBNR	$ 56
Cumulative number of claims | Claim	29,070
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 197	134	$ 71
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	1	(7)
IBNR, Total	(6)
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	388	397
IBNR	$ 153
Cumulative number of claims | Claim	32,575
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 168	$ 83
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(9)
IBNR, Total	(9)
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2022
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	437
IBNR	$ 263
Cumulative number of claims | Claim	30,229
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 112