Reinsurance - Voluntary Reinsurance Receivables by Financial Strength (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	$ 4,823
Reinsurance collateral	3,600	$ 3,700
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	576
Gateway Rivers Insurance Company
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	410
A- to A++
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	4,047
B- to B++
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	769
Insolvent
Voluntary Reinsurance Receivables [Abstract]
Voluntary reinsurance receivables	$ 7