Liability for Unpaid Claims and CAE - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Liability for Unpaid Claims and CAE
Unum US Group Long-term Disability Reserve Reduction, Before Tax	$ (121.0)	$ (215.0)
Unum US Group Life Reserve Reduction, Before Tax	(34.0)
Closed Block Long-term Care Reserve Increase		2.1
Closed Block Individual Disability Reserve Increase, Before Tax		6.4
Net Reduction in Unpaid Claims as a Result of Assumption Updates, Before Tax	(155.0)	(206.5)
Reinsurance Recoverables, Incurred but Not Reported Claims	8,401.4	8,854.8	$ 8,697.8		$ 8,378.9
Phase 2 | Closed Block Individual Disability Reinsurance Transaction
Liability for Unpaid Claims and CAE
Reinsurance Recoverables, Incurred but Not Reported Claims				$ 990.0
Increase in Benefits and Change in Reserves for Future Benefits	$ 133.1	$ 133.1