Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Commercial Auto (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 ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2012	$ 3,830	$ 4,216	$ 4,584
Total net liability for unpaid claim and claim adjustment expenses	19,205	18,701	17,885	$ 17,965
Property and casualty
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total net liability for unpaid claim and claim adjustment expenses	15,270	14,195
Commercial Auto
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	2,582
IBNR	433
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	1,928
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	654
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2012	5
Liability for unallocated claim adjustment expenses for accident years presented	14
Total net liability for unpaid claim and claim adjustment expenses	673
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	52	31	(17)
Total net development for accident years prior to 2012	1	2	(7)
Total unallocated claim adjustment expense development	0	0	(1)
Total	53	33	(25)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2012
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	295	296	297	299	$ 299	$ 307	$ 303	$ 299	$ 289	$ 275
IBNR	$ 1
Cumulative number of claims | Claim	46,288
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 292	291	291	290	285	282	259	220	160	$ 78
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)	(1)	(2)	0	(8)	4	4	10	14
IBNR, Total	20
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	241	241	241	245	245	249	265	265	246
IBNR	$ 2
Cumulative number of claims | Claim	39,430
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 239	239	238	234	225	200	168	135	$ 74
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	0	0	(4)	0	(4)	(16)	0	19
IBNR, Total	(5)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2014
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	202	201	201	205	205	212	223	234
IBNR	$ 2
Cumulative number of claims | Claim	33,628
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 199	198	196	187	166	137	102	$ 64
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	1	0	(4)	0	(7)	(11)	(11)
IBNR, Total	(32)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	183	181	183	190	190	199	201
IBNR	$ 3
Cumulative number of claims | Claim	30,427
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 178	175	172	153	130	96	$ 52
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	2	(2)	(7)	0	(9)	(2)
IBNR, Total	(18)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	195	190	186	186	186	198
IBNR	$ 3
Cumulative number of claims | Claim	30,449
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 185	175	154	126	93	$ 52
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	5	4	0	0	(12)
IBNR, Total	(3)
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	232	221	200	198	199
IBNR	$ 5
Cumulative number of claims | Claim	30,940
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 203	178	150	107	$ 58
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	11	21	2	(1)
IBNR, Total	33
Commercial Auto | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	245	227	227	229
IBNR	$ 8
Cumulative number of claims | Claim	34,292
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 212	175	128	$ 66
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	18	0	(2)
IBNR, Total	16
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	289	266	257
IBNR	$ 31
Cumulative number of claims | Claim	37,142
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 203	147	$ 77
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	23	9
IBNR, Total	32
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	303	310
IBNR	$ 107
Cumulative number of claims | Claim	28,837
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 134	$ 71
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(7)
IBNR, Total	(7)
Commercial Auto | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	397
IBNR	$ 271
Cumulative number of claims | Claim	27,182
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 83