Claims Development - Commercial Auto (Details) reported_claim in Thousands, $ in Millions	Dec. 31, 2022 USD ($) reported_claim	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	$ 3,312
Liabilities for loss and ALAE, net of reinsurance	7,967
Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	2,332
Cumulative paid losses and ALAE, net of reinsurance	1,581
All outstanding liabilities before, net of reinsurance	40
Liabilities for loss and ALAE, net of reinsurance	791
2018 | Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	444	$ 440	$ 442	$ 442	$ 453
Total of incurred but not reported liabilities plus expected development on reported losses	$ 9
Cumulative number of reported claims | reported_claim	49
Cumulative paid losses and ALAE, net of reinsurance	$ 411	378	337	266	$ 184
2019 | Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	469	453	451	452
Total of incurred but not reported liabilities plus expected development on reported losses	$ 18
Cumulative number of reported claims | reported_claim	46
Cumulative paid losses and ALAE, net of reinsurance	$ 395	333	268	$ 183
2020 | Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	384	391	424
Total of incurred but not reported liabilities plus expected development on reported losses	$ 37
Cumulative number of reported claims | reported_claim	36
Cumulative paid losses and ALAE, net of reinsurance	$ 280	214	$ 154
2021 | Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	477	470
Total of incurred but not reported liabilities plus expected development on reported losses	$ 91
Cumulative number of reported claims | reported_claim	39
Cumulative paid losses and ALAE, net of reinsurance	$ 278	$ 179
2022 | Commercial Auto Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	558
Total of incurred but not reported liabilities plus expected development on reported losses	$ 181
Cumulative number of reported claims | reported_claim	37
Cumulative paid losses and ALAE, net of reinsurance	$ 217