Liability for Unpaid Claims and CAE - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Liability for Unpaid Claims and CAE Narrative Information
Reinsurance Recoverables, Incurred but Not Reported Claims	$ 9,225.8	$ 8,378.9	$ 2,260.7	$ 2,246.8
Closed Block Individual Disability Reinsurance Transaction | Phase 2
Liability for Unpaid Claims and CAE Narrative Information
Increase in Benefits and Change in Reserves for Future Benefits	133.1
Reinsurance Recoverables, Incurred but Not Reported Claims	$ 990.0