Schedule 4 - Reinsurance Schedule (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Premiums, Life Insurance in Force	$ 20,889.0				$ 20,209.8				$ 20,889.0	$ 20,209.8	$ 20,565.9
Direct Premiums Earned									2,171.7	1,970.1	1,831.1
Ceded Premiums, Life Insurance in Force	486.9				514.2				486.9	514.2	541.5
Ceded to Other Companies									19.0	20.6	26.0
Assumed Premiums, Life Insurance in Force	195.0				205.7				195.0	205.7	217.8
Assumed Premiums Earned									67.3	60.1	57.1
Premiums, Net, Life Insurance in Force	20,597.1				19,901.3				20,597.1	19,901.3	20,242.2
Net Amount	$ 561.4	$ 558.9	$ 553.7	$ 546.0	$ 541.5	$ 536.7	$ 500.1	$ 431.3	$ 2,220.0	$ 2,009.6	$ 1,862.2
Life Insurance in Force Premiums, Percentage Assumed to Net	0.90%				1.00%				0.90%	1.00%	1.10%
Premiums, Percentage Assumed to Net									3.00%	3.00%	3.10%
Life Insurance Product Line [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Premiums Earned									$ 381.4	$ 374.1	$ 387.5
Ceded to Other Companies									1.4	1.4	1.5
Assumed Premiums Earned									1.3	1.4	1.6
Net Amount									$ 381.3	$ 374.1	$ 387.6
Premiums, Percentage Assumed to Net									0.30%	0.40%	0.40%
Accident and Health Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Premiums Earned									$ 144.9	$ 139.8	$ 146.3
Ceded to Other Companies									0.5	0.5	0.5
Assumed Premiums Earned									5.3	5.6	2.8
Net Amount									$ 149.7	$ 144.9	$ 148.6
Premiums, Percentage Assumed to Net									3.50%	3.90%	1.90%
Property, Liability and Casualty Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Premiums Earned									$ 1,645.4	$ 1,456.2	$ 1,297.3
Ceded to Other Companies									17.1	18.7	24.0
Assumed Premiums Earned									60.7	53.1	52.7
Net Amount									$ 1,689.0	$ 1,490.6	$ 1,326.0
Premiums, Percentage Assumed to Net									3.60%	3.60%	4.00%