Claims Development - Homeowner (Details) reported_claim in Thousands, $ in Millions	Dec. 31, 2021 USD ($) reported_claim	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	$ 3,118
Liabilities for loss and ALAE, net of reinsurance	6,917
Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	2,169
Cumulative paid losses and ALAE, net of reinsurance	1,893
All outstanding liabilities before, net of reinsurance	5
Liabilities for loss and ALAE, net of reinsurance	281
2017 | Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	389	$ 387	$ 385	$ 383	$ 356
Total of incurred but not reported liabilities plus expected development on reported losses	$ 1
Cumulative number of reported claims | reported_claim	27
Cumulative paid losses and ALAE, net of reinsurance	$ 386	384	378	356	$ 277
2018 | Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	388	387	386	370
Total of incurred but not reported liabilities plus expected development on reported losses	$ 5
Cumulative number of reported claims | reported_claim	24
Cumulative paid losses and ALAE, net of reinsurance	$ 381	378	368	$ 268
2019 | Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	422	421	432
Total of incurred but not reported liabilities plus expected development on reported losses	$ 7
Cumulative number of reported claims | reported_claim	22
Cumulative paid losses and ALAE, net of reinsurance	$ 407	391	$ 303
2020 | Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	475	497
Total of incurred but not reported liabilities plus expected development on reported losses	$ 16
Cumulative number of reported claims | reported_claim	23
Cumulative paid losses and ALAE, net of reinsurance	$ 434	$ 326
2021 | Home Owner Line | Personal Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	495
Total of incurred but not reported liabilities plus expected development on reported losses	$ 95
Cumulative number of reported claims | reported_claim	17
Cumulative paid losses and ALAE, net of reinsurance	$ 285