Schedule 4 - Reinsurance Schedule (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums, Life Insurance in Force	$ 19,435.1				$ 19,208.7				$ 19,435.1	$ 19,208.7	$ 20,889.0
Ceded Premiums, Life Insurance in Force	436.4				455.2				436.4	455.2	486.9
Ceded to Other Companies									31.6	18.2	19.0
Assumed Premiums, Life Insurance in Force	172.7				184.0				172.7	184.0	195.0
Premiums, Net, Life Insurance in Force	19,171.4				18,937.5				19,171.4	18,937.5	20,597.1
Net Amount	$ 1,063.6	$ 1,052.9	$ 658.1	$ 609.8	$ 605.9	$ 598.2	$ 582.5	$ 563.4	$ 3,384.4	$ 2,350.0	$ 2,220.0
Life Insurance in Force Premiums, Percentage Assumed to Net	0.90%				1.00%				0.90%	1.00%	0.90%
Life Insurance Product Line [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned									$ 378.2	$ 366.8	$ 381.4
Ceded to Other Companies									1.2	1.4	1.4
Assumed Premiums Earned									1.0	1.1	1.3
Net Amount									$ 378.0	$ 366.5	$ 381.3
SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net									0.30%	0.30%	0.30%
Accident and Health Insurance [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned									$ 174.3	$ 171.0	$ 144.9
Ceded to Other Companies									1.7	1.5	0.5
Assumed Premiums Earned									5.3	5.4	5.3
Net Amount									$ 177.9	$ 174.9	$ 149.7
SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net									3.00%	3.10%	3.50%
Property, Liability and Casualty Insurance [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned									$ 2,778.3	$ 1,757.5	$ 1,645.4
Ceded to Other Companies									28.7	15.3	17.1
Assumed Premiums Earned									78.9	66.4	60.7
Net Amount									$ 2,828.5	$ 1,808.6	$ 1,689.0
SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net									2.80%	3.70%	3.60%
Operating Segments [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned									$ 3,330.8	$ 2,295.3	$ 2,171.7
Ceded to Other Companies									31.6	18.2	19.0
Assumed Premiums Earned									85.2	72.9	67.3
Net Amount									$ 3,384.4	$ 2,350.0	$ 2,220.0
SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net									2.50%	3.10%	3.00%