Allowance for Expected Credit Losses (Details) - Narrative - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reinsurance recoverables, credit quality indicator
Reinsurance recoverables, after deducting mandatory pools and associations and before allowances for expected credit losses	$ 8,593	$ 8,496
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables [Member] | Reinsurer Group Rated by A.M. Best [Member] | A.M. Best, Rating Provided [Member]
Reinsurance recoverables, credit quality indicator
Reinsurance recoverables, after deducting mandatory pools and associations and before allowances for expected credit losses	$ 5,930
Concentration risk percentage	87.00%
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables [Member] | Reinsurer Group Not Rated by A.M. Best [Member]
Reinsurance recoverables, credit quality indicator
Concentration risk percentage	13.00%
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables [Member] | Captive Insurance Companies [Member]
Reinsurance recoverables, credit quality indicator
Concentration risk percentage	6.00%
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables [Member] | Voluntary Pools [Member]
Reinsurance recoverables, credit quality indicator
Concentration risk percentage	1.00%
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables [Member] | Other Companies [Member]
Reinsurance recoverables, credit quality indicator
Concentration risk percentage	6.00%
Reinsurer Concentration Risk [Member] | Reinsurance Recoverables Rated by A.M. Best [Member] | Reinsurer Group Rated by A.M. Best [Member] | A.M. Best, A- Rating Or Better [Member]
Reinsurance recoverables, credit quality indicator
Concentration risk percentage	94.00%