Income Taxes - Schedule of Temporary Differences That Give Rise to Net Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred Income Tax Assets:
Insurance Reserves	$ 16.2	$ 17.0
Unearned Premium Reserves	64.5	59.1
Tax Capitalization of Policy Acquisition Costs	44.6	44.0
Payroll and Employee Benefit Accruals	35.0	49.6
Net Operating Loss Carryforwards	3.3	5.5
Other	12.5	11.2
Total Deferred Income Tax Assets	176.1	186.4
Deferred Income Tax Liabilities:
Investments	155.6	33.2
Deferred Policy Acquisition Costs	112.9	98.7
Life VIF and P&C Customer Relationships	5.3	6.0
Goodwill and Other Intangible Assets Acquired	39.3	45.2
Depreciable Assets	37.6	27.1
Other	3.6	2.4
Total Deferred Income Tax Liabilities	354.3	212.6
Net Deferred Income Tax Liabilities	$ 178.2	$ 26.2