Insurance Liabilities - Discounting Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying amount of liabilities for unpaid claims	$ 1,129.0
Aggregate amount of discount	217.7
Long-Term Disability/Group Life Waiver
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying amount of liabilities for unpaid claims	1,020.0	$ 1,003.2
Aggregate amount of discount	217.7	226.2
Interest accretion	$ 34.5	$ 35.0	$ 36.3
Long-Term Disability/Group Life Waiver | Minimum
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Discount rate	3.30%	3.30%
Long-Term Disability/Group Life Waiver | Maximum
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Discount rate	7.00%	7.00%
Dental/Vision/Short-Term Disability/Critical Illness/Accident
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying amount of liabilities for unpaid claims	$ 59.3	$ 53.6
Group Life
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying amount of liabilities for unpaid claims	$ 49.7	$ 47.3