Property Casualty Loss and Loss Expense - Claims Development - Homeowner (Details) reported_claim in Thousands, $ in Millions	Dec. 31, 2023 USD ($) reported_claim	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	$ 3,496
Liabilities for loss and ALAE, net of reinsurance	8,535
Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	2,576
Cumulative paid losses and ALAE, net of reinsurance	2,231
All outstanding liabilities before, net of reinsurance	6
Liabilities for loss and ALAE, net of reinsurance	351
2019 | Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	418	$ 418	$ 422	$ 421	$ 432
Total of incurred but not reported liabilities plus expected development on reported losses	$ 2
Cumulative number of reported claims | reported_claim	22
Cumulative paid losses and ALAE, net of reinsurance	$ 414	411	407	391	$ 303
2020 | Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	471	470	475	497
Total of incurred but not reported liabilities plus expected development on reported losses	$ 3
Cumulative number of reported claims | reported_claim	23
Cumulative paid losses and ALAE, net of reinsurance	$ 464	453	434	$ 326
2021 | Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	440	449	495
Total of incurred but not reported liabilities plus expected development on reported losses	$ 4
Cumulative number of reported claims | reported_claim	19
Cumulative paid losses and ALAE, net of reinsurance	$ 424	405	$ 285
2022 | Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	505	552
Total of incurred but not reported liabilities plus expected development on reported losses	$ 21
Cumulative number of reported claims | reported_claim	20
Cumulative paid losses and ALAE, net of reinsurance	$ 461	$ 299
2023 | Homeowner | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	742
Total of incurred but not reported liabilities plus expected development on reported losses	$ 116
Cumulative number of reported claims | reported_claim	21
Cumulative paid losses and ALAE, net of reinsurance	$ 468