Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Commercial Auto - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Commercial Auto - Commercial $ in Millions	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 ($)	Dec. 31, 2013 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,771
IBNR	521
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	243	$ 241	$ 241	$ 241	$ 245	$ 245	$ 249	$ 265	$ 265	$ 246
IBNR	$ 3
Cumulative Number of Claims | claim	39,431
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 201	202	201	201	205	205	212	223	$ 234
IBNR	$ 1
Cumulative Number of Claims | claim	33,631
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 182	183	181	183	190	190	199	$ 201
IBNR	$ 3
Cumulative Number of Claims | claim	30,430
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 200	195	190	186	186	186	$ 198
IBNR	$ 7
Cumulative Number of Claims | claim	30,452
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 239	232	221	200	198	$ 199
IBNR	$ 3
Cumulative Number of Claims | claim	30,947
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 254	245	227	227	$ 229
IBNR	$ 5
Cumulative Number of Claims | claim	34,319
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 323	289	266	$ 257
IBNR	$ 27
Cumulative Number of Claims | claim	37,237
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 304	303	$ 310
IBNR	$ 56
Cumulative Number of Claims | claim	29,070
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 388	$ 397
IBNR	$ 153
Cumulative Number of Claims | claim	32,575
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 437
IBNR	$ 263
Cumulative Number of Claims | claim	30,229