Schedule 2 - Parent Company Financial Statements - Statements of Income (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
Condensed Financial Statements, Captions [Line Items]
Gain on Cash Flow Hedge									$ 0.6	$ 0.0	$ 0.0
Net Investment Income	$ 79.9	$ 77.7	$ 73.7	$ 67.0	$ 79.4	$ 75.9	$ 76.7	$ 70.6	298.3	302.6	309.1
Net Realized Gains (Losses) on Sales of Investments	9.1	11.6	5.6	6.8	9.4	5.3	34.0	3.4	33.1	52.1	39.1
Net Impairment Losses Recognized in Earnings	(8.7)	(8.3)	(6.4)	(9.3)	(14.7)	(3.3)	(2.2)	(7.0)	(32.7)	(27.2)	(15.2)
Total Revenues	642.7	640.7	627.2	611.3	617.0	615.4	609.2	499.2	2,521.9	2,340.8	2,196.6
Loss from Early Extinguishment of Debt					0.0	0.0	0.0	9.1	0.0	9.1	0.0
Total Expenses	602.1	673.9	624.6	617.8	618.6	565.6	574.9	481.4	2,518.4	2,240.5	2,036.4
Income Tax Benefit	(11.5)	14.9	1.5	4.3	2.9	(11.8)	(6.9)	(4.3)	9.2	(20.1)	(47.6)
Net Income	$ 31.2	$ (16.3)	$ 4.0	$ (2.1)	$ 4.6	$ 37.9	$ 29.7	$ 13.5	16.8	85.7	114.5
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Gain on Cash Flow Hedge									0.6	0.0	0.0
Net Investment Income									2.0	1.7	0.9
Net Realized Gains (Losses) on Sales of Investments									0.1	(0.1)	(0.2)
Net Impairment Losses Recognized in Earnings									0.0	(1.6)	(1.7)
Total Revenues									2.1	0.0	(1.0)
Interest Expense									45.2	47.3	47.9
Loss from Early Extinguishment of Debt									0.0	9.1	0.0
Other Operating (Benefits) Expenses									(6.1)	17.6	2.7
Total Expenses									39.1	74.0	50.6
Loss before Income Taxes and Equity in Net Income of Subsidiaries									(37.0)	(74.0)	(51.6)
Income Tax Benefit									13.4	26.5	18.9
Loss before Equity in Net Income of Subsidiaries									(23.6)	(47.5)	(32.7)
Equity in Net Income of Subsidiaries									40.4	133.2	147.2
Net Income									$ 16.8	$ 85.7	$ 114.5