Income Taxes - Schedule of Temporary Differences That Give Rise to Net Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Income Tax Assets:
Insurance Reserves	$ 83.4	$ 83.0
Unearned Premium Reserves	42.1	41.7
Tax Capitalization of Policy Acquisition Costs	70.7	71.5
Payroll and Employee Benefit Accruals	60.5	72.0
Net Operating Loss Carryforward	52.2	30.5
Other	13.2	15.7
Total Deferred Income Tax Assets	322.1	314.4
Deferred Income Tax Liabilities:
Investments	113.0	109.8
Deferred Policy Acquisition Costs	116.2	110.7
Life VIF and P&C Customer Relationships	13.5	15.5
Goodwill and Other Intangible Assets Acquired	37.1	37.0
Depreciable Assets	12.5	7.3
Other	4.0	2.2
Total Deferred Income Tax Liabilities	296.3	282.5
Net Deferred Income Tax Liabilities	$ 25.8	$ 31.9