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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities:
Net Income		$ 4.6	$ 37.9	$ 29.7	$ 13.5	$ 65.4	$ 4.7	$ 9.3	$ 35.1	$ 85.7	$ 114.5	$ 217.7
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
Net Realized (Gains) Losses on Sales of Investments		(9.4)	(5.3)	(34.0)	(3.4)	(21.0)	(8.0)	(3.5)	(6.6)	(52.1)	(39.1)	(99.1)
Net Impairment Losses Recognized in Earnings		14.7	3.3	2.2	7.0	6.5	$ 3.8	$ 4.1	0.8	27.2	15.2	13.9
Loss from Early Extinguishment of Debt		0.0	$ 0.0	$ 0.0	9.1					9.1	0.0	0.0
Other, Net										32.2	16.4	36.1
Net Cash Provided by Operating Activities										215.0	133.6	122.1
Investing Activities:
Capital Contributed to Subsidiary	$ 75.0
Sales, Paydowns and Maturities of Fixed Maturities										627.8	573.7	664.4
Sales of Equity Securities										238.4	245.3	182.1
Sales of Fair Value Option Investments										0.0	6.9	0.0
Purchases of Fair Value Option Investments										(111.0)	(60.9)	0.0
Payments to Acquire Businesses, Net of Cash Acquired										(57.6)	0.0	0.0
Change in Short-term Investments										104.9	(63.9)	41.8
Net Cash Provided (Used) by Investing Activities										(28.6)	(104.3)	4.8
Notes Payable Proceeds:
Cash Dividends Paid										(49.7)	(51.8)	(54.9)
Common Stock Repurchases										(45.0)	(114.0)	(100.4)
Cash Exercise of Stock Options										3.9	0.5	1.7
Net Cash Used by Financing Activities										(100.8)	(19.7)	(156.7)
Increase (Decrease) in Cash										85.6	9.6	(29.8)
Cash, Beginning of Year					76.1				66.5	76.1	66.5	96.3
Cash, End of Year		161.7				76.1				161.7	76.1	66.5
Purchases of Fixed Maturities										681.3	553.0	744.5
Parent Company [Member]
Operating Activities:
Net Income										85.7	114.5	217.7
Adjustment Required to Reconcile Net Income to Net Cash Provided by Operations:
Equity in Net Income of Subsidiaries										(133.2)	(147.2)	(256.7)
Cash Dividends from Subsidiaries										285.0	159.1	95.0
Cash Contribution to Defined Benefit Plan										0.0	0.0	(55.0)
Net Realized (Gains) Losses on Sales of Investments										0.1	0.2	(0.6)
Net Impairment Losses Recognized in Earnings										1.6	1.7	0.0
Loss from Early Extinguishment of Debt										9.1	0.0	0.0
Other, Net										41.6	10.5	67.3
Net Cash Provided by Operating Activities										289.9	138.8	67.7
Investing Activities:
Capital Contributed to Subsidiary										105.0	0.0	0.0
Capital Distribution from Subsidiary										0.0	1.1	50.5
Sales, Paydowns and Maturities of Fixed Maturities										11.8	11.5	0.0
Sales of Equity Securities										9.4	15.1	0.0
Sales of Fair Value Option Investments										0.0	6.9	0.0
Purchases of Fair Value Option Investments										(111.0)	(60.9)	0.0
Payments to Acquire Businesses, Net of Cash Acquired										(71.0)	0.0	0.0
Change in Short-term Investments										90.3	(94.3)	52.7
Net Cash Provided (Used) by Investing Activities										(190.3)	(120.6)	103.2
Notes Payable Proceeds:
Net Proceeds from Issuance of Subordinated Debentures										247.3	144.0	0.0
Cash Dividends Paid										(49.7)	(51.8)	(54.9)
Common Stock Repurchases										(45.0)	(114.0)	(100.4)
Cash Exercise of Stock Options										3.9	0.5	1.7
Excess Tax Benefits on Share Based Awards										0.7	0.2	1.3
Net Cash Used by Financing Activities										(101.6)	(21.1)	(152.3)
Increase (Decrease) in Cash										(2.0)	(2.9)	18.6
Cash, Beginning of Year					$ 17.9				$ 20.8	17.9	20.8	2.2
Cash, End of Year		$ 15.9				$ 17.9				15.9	17.9	20.8
Purchases of Fixed Maturities										14.8	0.0	0.0
Notes Payable Payments:
Repayments of Debt										$ 258.8	$ 0.0	$ 0.0