Schedule 3 - Supplementary Insurance Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Premiums		$ 2,220.0	$ 2,009.6	$ 1,862.2
Other Income		3.2	3.7	1.4
Net Investment Income		298.3	302.6	309.1
Insurance Claims and Policyholders' Benefits		1,780.8	1,467.5	1,261.7
Amortization of Deferred Policy Acquisition Costs		299.3	257.4	235.4
Other Insurance Expenses		348.0	387.8	393.0
Deferred Policy Acquisition Costs		332.0	316.4
Insurance Reserves		4,406.7	4,203.8
Unearned Premiums		618.7	613.1
Property and Casualty Insurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Premiums		1,614.8	1,415.2	1,249.5
Premiums Written		1,620.9	1,406.2	1,189.1
Other Income		0.5	0.6	0.5
Net Investment Income		72.4	73.3	72.7
Insurance Claims and Policyholders' Benefits		1,319.2	1,086.2	887.3
Amortization of Deferred Policy Acquisition Costs		252.1	213.1	187.5
Other Insurance Expenses		133.6	155.0	166.2
Deferred Policy Acquisition Costs		82.1	80.7
Insurance Reserves		884.1	800.5
Unearned Premiums		592.0	586.1
Life and Health Insurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Premiums	[1]	605.2	594.4	612.7
Other Income	[1]	2.8	2.4	0.9
Net Investment Income	[1]	213.2	214.2	218.7
Insurance Claims and Policyholders' Benefits	[1]	461.6	381.3	374.4
Amortization of Deferred Policy Acquisition Costs	[1]	47.2	44.3	47.9
Other Insurance Expenses	[1]	266.7	275.7	268.1
Deferred Policy Acquisition Costs	[1]	249.9	235.7
Insurance Reserves	[1]	3,479.8	3,346.2
Unearned Premiums	[1]	26.7	27.0
Other Segments [Member]
Supplementary Insurance Information, by Segment [Line Items]
Premiums		0.0	0.0	0.0
Other Income		(0.1)	0.7	0.0
Net Investment Income		12.7	15.1	17.7
Insurance Claims and Policyholders' Benefits		0.0	0.0	0.0
Amortization of Deferred Policy Acquisition Costs		0.0	0.0	0.0
Other Insurance Expenses		(52.3)	(42.9)	$ (41.3)
Deferred Policy Acquisition Costs		0.0	0.0
Insurance Reserves		42.8	57.1
Unearned Premiums		$ 0.0	$ 0.0

[1] The Company’s Life & Health Insurance employee-agents also market certain property and casualty insurance products under common management. Accordingly, the Company includes the results of these property and casualty insurance products in its Life & Health Insurance segment.