Reinsurance, Voluntary Reinsurance Receivables by Financial Strength (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Voluntary Reinsurance Receivables [Abstract]
Reinsurance collateral	$ 4,000	$ 3,300
Voluntary reinsurance receivables	4,802
Subsidiaries of Berkshire Hathaway Insurance Group
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	1,800
Cavello Bay Reinsurance Limited
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	612
Gateway Rivers Insurance Company
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	425
A- to A++
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	3,812
B- to B++
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	987
Insolvent
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	$ 3