Schedule 2 - Parent Company Financial Statements - Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Net Investment Income	$ 102.7	$ 92.1	$ 67.8	$ 85.6	$ 93.9	$ 91.7	$ 96.0	$ 82.7	$ 348.2	$ 364.3	$ 340.9
Income (Loss) from Change in Fair Value of Equity and Convertible Securities	73.1	45.2	71.6	(117.8)	39.2	9.8	25.5	64.4	72.1	138.9	(64.3)
Net Realized Gains on Sales of Investments	(0.1)	10.0	11.7	16.5	2.8	1.7	21.3	16.1	38.1	41.9	26.4
Impairment Losses	0.5	(1.0)	(7.0)	(12.0)	(1.7)	(1.8)	(6.7)	(3.6)	(19.5)	(13.8)	(4.5)
Total Revenues	1,392.1	1,353.7	1,230.9	1,229.0	1,283.7	1,243.8	1,275.4	1,236.3	5,205.7	5,039.2	3,725.1
Interest Expense									36.0	42.5	43.3
Loss from Early Extinguishment of Debt						5.8			0.0	5.8	0.0
Pension Settlement Expense									64.1	0.0	0.0
Total Expenses	1,271.5	1,201.6	1,071.2	1,151.3	1,126.8	1,082.3	1,126.9	1,041.6	4,695.6	4,377.6	3,526.0
Income Tax Benefit	(23.1)	(29.8)	(33.6)	(13.7)	(32.2)	(32.5)	(26.4)	(39.4)	(100.2)	(130.5)	(10.7)
Net Income	$ 97.5	$ 122.3	$ 126.1	$ 64.0	$ 124.7	$ 129.0	$ 122.1	$ 155.3	409.9	531.1	190.1
Parent Company
Condensed Income Statements, Captions [Line Items]
Net Investment Income									1.4	2.1	2.5
Income (Loss) from Change in Fair Value of Equity and Convertible Securities									4.3	1.6	1.4
Net Realized Gains on Sales of Investments									0.1	0.3	(0.7)
Total Revenues									5.8	4.0	3.2
Interest Expense									24.2	28.5	37.6
Loss from Early Extinguishment of Debt									0.0	5.8	0.0
Defined Benefit Plan, Benefit Obligation, Payment for Settlement									(64.1)
Pension Settlement Expense									64.1	0.0	0.0
Other Operating (Benefits) Expenses									(3.6)	4.0	26.3
Total Expenses									84.7	38.3	63.9
Loss before Income Taxes and Equity in Net Income of Subsidiaries									(78.9)	(34.3)	(60.7)
Income Tax Benefit									13.4	9.4	12.2
Loss before Equity in Net Income of Subsidiaries									(65.5)	(24.9)	(48.5)
Equity in Net Income of Subsidiaries									475.4	556.0	238.6
Net Income									$ 409.9	$ 531.1	$ 190.1