Schedule 2 - Parent Company Financial Statements - Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	May 07, 2015	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
Operating Activities:
Net Income		$ 31.2	$ (16.3)	$ 4.0	$ (2.1)	$ 4.6	$ 37.9	$ 29.7	$ 13.5	$ 16.8	$ 85.7	$ 114.5
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
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
Loss from Early Extinguishment of Debt						0.0	$ 0.0	$ 0.0	9.1	0.0	9.1	0.0
Other, Net										0.7	32.2	16.4
Net Cash Provided by Operating Activities										240.5	215.0	133.6
Investing Activities:
Capital Contributed to Subsidiary	$ 75.0
Sales, Paydowns and Maturities of Fixed Maturities										532.3	627.8	573.7
Sales of Equity Securities										158.9	238.4	245.3
Sales of Fair Value Option Investments										72.2	0.0	6.9
Purchases of Fair Value Option Investments										(21.0)	(111.0)	(60.9)
Payments to Acquire Businesses, Net of Cash Acquired										0.0	(57.6)	0.0
Change in Short-term Investments										(18.0)	104.9	(63.9)
Net Cash Used by Investing Activities										(238.1)	(28.6)	(104.3)
Notes Payable Proceeds:
Cash Dividends Paid										(49.2)	(49.7)	(51.8)
Common Stock Repurchases										(3.8)	(45.0)	(114.0)
Cash Exercise of Stock Options										3.5	3.9	0.5
Net Cash Used by Financing Activities										(48.4)	(100.8)	(19.7)
Decrease in Cash										(46.0)	85.6	9.6
Cash, Beginning of Year					161.7				76.1	161.7	76.1	66.5
Cash, End of Year		115.7				161.7				115.7	161.7	76.1
Purchases of Fixed Maturities										850.3	681.3	553.0
Parent Company [Member]
Operating Activities:
Net Income										16.8	85.7	114.5
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
Equity in Net Income of Subsidiaries										(40.4)	(133.2)	(147.2)
Cash Dividends from Subsidiaries										77.7	285.0	159.1
Cash Received for Benefit Plan from Subsidiary										1.4	0.0	0.0
Cash Contribution to Defined Benefit Plan										(9.0)	0.0	0.0
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
Loss from Early Extinguishment of Debt										0.0	9.1	0.0
Other, Net										(9.3)	41.6	10.5
Net Cash Provided by Operating Activities										37.1	289.9	138.8
Investing Activities:
Capital Contributed to Subsidiary										52.9	105.0	0.0
Capital Distribution from Subsidiary										0.0	0.0	1.1
Sales, Paydowns and Maturities of Fixed Maturities										73.5	11.8	11.5
Sales of Equity Securities										3.5	9.4	15.1
Sales of Fair Value Option Investments										72.2	0.0	6.9
Purchases of Fair Value Option Investments										(21.0)	(111.0)	(60.9)
Payments to Acquire Businesses, Net of Cash Acquired										0.0	(71.0)	0.0
Change in Short-term Investments										14.8	90.3	(94.3)
Net Cash Used by Investing Activities										12.2	(190.3)	(120.6)
Notes Payable Proceeds:
Net Proceeds from Issuance of Subordinated Debentures										0.0	247.3	144.0
Cash Dividends Paid										(49.2)	(49.7)	(51.8)
Common Stock Repurchases										(3.8)	(45.0)	(114.0)
Cash Exercise of Stock Options										3.5	3.9	0.5
Excess Tax Benefits on Share Based Awards										0.0	0.7	0.2
Net Cash Used by Financing Activities										(49.5)	(101.6)	(21.1)
Decrease in Cash										(0.2)	(2.0)	(2.9)
Cash, Beginning of Year					$ 15.9				$ 17.9	15.9	17.9	20.8
Cash, End of Year		$ 15.7				$ 15.9				15.7	15.9	17.9
Purchases of Fixed Maturities										77.9	14.8	0.0
Notes Payable Payments:
Repayments of Debt										$ 0.0	$ 258.8	$ 0.0