Insurance Liabilities - Reconciliation of Unpaid Claims to Liability for Unpaid Claims Table (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	$ 1,309.2
Reconciling items
Reinsurance recoverable on unpaid claims	57.3
Impact of discounting	(215.0)
Liability for unpaid claims - short duration contracts	1,151.5
Insurance contracts other than short duration	1,214.0
Liability for unpaid claims	2,365.5	$ 2,252.7	$ 2,130.5	$ 2,001.3
Long-Term Disability/Group Life Waiver
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	1,188.5
Reconciling items
Reinsurance recoverable on unpaid claims	56.4
Impact of discounting	(215.0)	(217.7)
Liability for unpaid claims - short duration contracts	1,029.9	1,020.0
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	71.2
Reconciling items
Liability for unpaid claims - short duration contracts	71.2	59.3
Group Life
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities for unpaid claims	49.5
Reconciling items
Reinsurance recoverable on unpaid claims	0.9
Liability for unpaid claims - short duration contracts	$ 50.4	$ 49.7