Insurance Liabilities - Reconciliation of Unpaid Claims to Liability for Unpaid Claims Table (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	$ 1,333.2
Reconciling items
Reinsurance recoverable on unpaid claims	53.4
Impact of discounting	(214.5)
Liability for unpaid claims - short duration contracts	1,172.1
Insurance contracts other than short duration	1,362.8
Liability for unpaid claims	2,534.9	$ 2,365.5	$ 2,252.7	$ 2,130.5
Long-Term Disability/Group Life Waiver
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	1,208.8
Reconciling items
Reinsurance recoverable on unpaid claims	53.3
Impact of discounting	(214.5)	(215.0)
Liability for unpaid claims - short duration contracts	1,047.6	1,029.9
Dental/Vision/Short-Term Disability/Critical Illness/Accident
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	70.4
Reconciling items
Liability for unpaid claims - short duration contracts	70.4	71.2
Group Life
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	54.0
Reconciling items
Reinsurance recoverable on unpaid claims	0.1
Liability for unpaid claims - short duration contracts	$ 54.1	$ 50.4