Claims Development - Commercial Property (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
Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	3,118
Cumulative paid losses and ALAE, net of reinsurance	2,698
All outstanding liabilities before, net of reinsurance	17
Liabilities for loss and ALAE, net of reinsurance	437
2017 | Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	572	$ 565	$ 556	$ 560	$ 587
Total of incurred but not reported liabilities plus expected development on reported losses	$ 2
Cumulative number of reported claims | reported_claim	18
Cumulative paid losses and ALAE, net of reinsurance	$ 567	560	547	522	$ 395
2018 | Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	597	590	603	630
Total of incurred but not reported liabilities plus expected development on reported losses	$ 6
Cumulative number of reported claims | reported_claim	18
Cumulative paid losses and ALAE, net of reinsurance	$ 589	576	559	$ 386
2019 | Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	600	606	621
Total of incurred but not reported liabilities plus expected development on reported losses	$ 9
Cumulative number of reported claims | reported_claim	17
Cumulative paid losses and ALAE, net of reinsurance	$ 579	561	$ 413
2020 | Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	742	855
Total of incurred but not reported liabilities plus expected development on reported losses	$ 43
Cumulative number of reported claims | reported_claim	23
Cumulative paid losses and ALAE, net of reinsurance	$ 637	$ 489
2021 | Commercial Property Line | Commercial Insurance
Claims Development
Incurred losses and ALAE, net of reinsurance for the years ended December 31,	607
Total of incurred but not reported liabilities plus expected development on reported losses	$ 49
Cumulative number of reported claims | reported_claim	13
Cumulative paid losses and ALAE, net of reinsurance	$ 326