Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net Income	$ 120.9	$ 16.8	$ 85.7
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Increase in Deferred Policy Acquisition Costs	(33.3)	(15.6)	(13.1)
Amortization of Intangible Assets Acquired	5.1	5.9	15.4
Equity in Earnings of Equity Method Limited Liability Investments	(24.8)	(7.5)	(19.0)
Distribution of Accumulated Earnings of Equity Method Limited Liability Investments	19.6	15.7	8.6
Decrease (Increase) in Value of Fair Value Option Investments reported in Investment Income	(1.3)	1.9	(0.3)
Amortization of Investment Securities and Depreciation of Investment Real Estate	16.7	16.2	16.1
Net Realized Gains on Sales of Investments	(56.5)	(33.1)	(52.1)
Net Impairment Losses Recognized in Earnings	14.3	32.7	27.2
Loss from Early Extinguishment of Debt	0.0	0.0	9.1
Depreciation of Property and Equipment	13.1	13.6	13.5
Write-off of Long-lived Assets	0.0	0.0	11.1
Decrease (Increase) in Other Receivables	(29.2)	(11.0)	49.6
Increase (Decrease) in Insurance Reserves	131.1	201.8	39.6
Increase (Decrease) in Unearned Premiums	35.2	5.6	(9.4)
Change in Income Taxes	28.9	(6.5)	(21.8)
Increase (Decrease) in Accrued Expenses and Other Liabilities	2.9	3.3	22.6
Other, Net	(2.1)	0.7	32.2
Net Cash Provided by Operating Activities	240.6	240.5	215.0
Investing Activities:
Sales, Paydowns and Maturities of Fixed Maturities	528.2	532.3	627.8
Purchases of Fixed Maturities	(710.1)	(850.3)	(681.3)
Sales of Equity Securities	342.0	158.9	238.4
Purchases of Equity Securities	(342.7)	(90.1)	(134.0)
Acquisition and Improvements of Investment Real Estate	(1.5)	(2.2)	(1.8)
Sales of Investment Real Estate	26.7	7.5	7.7
Sales of and Return of Investment of Equity Method Limited Liability Investments	48.1	41.0	32.9
Acquisitions of Equity Method Limited Liability Investments	(27.9)	(34.6)	(32.4)
Sales of Fair Value Option Investments	42.2	72.2	0.0
Purchases of Fair Value Option Investments	(7.0)	(21.0)	(111.0)
Decrease (Increase) in Short-term Investments	39.4	(18.0)	104.9
Acquisition of Businesses, Net of Cash Acquired	0.0	0.0	(57.6)
Increase in Other Investments	(4.5)	(5.7)	(3.2)
Purchase of Corporate-owned Life Insurance	0.0	(7.5)	(7.5)
Acquisition of Software	(35.5)	(17.6)	(8.9)
Other, Net	(2.8)	(3.0)	(2.6)
Net Cash Used by Investing Activities	(105.4)	(238.1)	(28.6)
Financing Activities:
Net Proceeds from Issuances of Debt	200.2	0.0	247.3
Repayments of Debt	(360.0)	0.0	(258.8)
Common Stock Repurchases	0.0	(3.8)	(45.0)
Dividends and Dividend Equivalents Paid	(49.5)	(49.2)	(49.7)
Cash Exercise of Stock Options	4.0	3.5	3.9
Other, Net	0.1	1.1	1.5
Net Cash Used by Financing Activities	(205.2)	(48.4)	(100.8)
Increase (Decrease) in Cash	(70.0)	(46.0)	85.6
Cash, Beginning of Year	115.7	161.7	76.1
Cash, End of Year	$ 45.7	$ 115.7	$ 161.7