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Reinsurance - Rollforward of credit loss allowance for reinsurance recoverables (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]    
Reinsurance recoverable, allowance for credit loss, beginning balance $ (3)  
Cumulative effect of change in accounting principle   $ (11)
Increase in the provision for credit losses (1)  
Write-offs 0  
Reinsurance recoverable, allowance for credit loss, ending balance $ (15)