Income Taxes - Schedule of Temporary Differences That Give Rise to Net Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Income Tax Assets:
Insurance Reserves	$ 55.7	$ 83.4
Unearned Premium Reserves	26.7	42.1
Tax Capitalization of Policy Acquisition Costs	41.9	70.7
Payroll and Employee Benefit Accruals	37.2	60.5
Net Operating Loss Carryforward	31.8	52.2
Other	3.7	13.2
Total Deferred Income Tax Assets	197.0	322.1
Deferred Income Tax Liabilities:
Investments	90.6	113.0
Deferred Policy Acquisition Costs	76.8	116.2
Life VIF and P&C Customer Relationships	6.9	13.5
Goodwill and Other Intangible Assets Acquired	22.3	37.1
Depreciable Assets	12.1	12.5
Other	3.1	4.0
Deferred Tax Liabilities, Gross	211.8	296.3
Total Deferred Income Tax Liabilities	$ (14.8)
Net Deferred Income Tax Asset		$ 25.8