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Reinsurance (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Feb. 05, 2021
Ceded Credit Risk [Line Items]        
Funds held under reinsurance agreements, liability $ 4,000 $ 3,300   $ 690
Largest recoverable from single reinsurer 5,463 4,457    
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations 3,058 3,158 $ 2,733  
Subsidiaries of Berkshire Hathaway Group        
Ceded Credit Risk [Line Items]        
Largest recoverable from single reinsurer 1,800      
Cavello Bay Reinsurance Limited        
Ceded Credit Risk [Line Items]        
Largest recoverable from single reinsurer 612      
Gateway Rivers Insurance Company        
Ceded Credit Risk [Line Items]        
Largest recoverable from single reinsurer 425      
Significant Captive Program        
Ceded Credit Risk [Line Items]        
Direct and ceded earned premiums 3,638 3,543 3,578  
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations $ 2,003 $ 2,375 $ 2,080