Insurance Expenses (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Expenses [Abstract]
Commissions									$ 425.6	$ 399.2	$ 357.6
General Expenses									194.1	209.0	241.1
Taxes, Licenses and Fees									52.8	48.8	44.2
Total Costs Incurred									672.5	657.0	642.9
Policy Acquisition Costs:
Deferred									(351.6)	(314.9)	(270.6)
Amortized									318.3	299.3	257.4
Net Policy Acquisition Costs Deferred									(33.3)	(15.6)	(13.2)
Amortization of Insurance in Force									5.1	5.9	15.4
Insurance Expenses	$ 159.1	$ 163.7	$ 163.5	$ 158.0	$ 158.5	$ 161.7	$ 167.8	$ 159.3	$ 644.3	$ 647.3	$ 645.1