Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash Flows from Operating Activities:
Net Income	$ 312,400,000	$ 406,400,000
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Net Realized Investment (Gains) Losses	(38,200,000)	(39,100,000)
Impairment Losses	20,000,000.0	12,100,000
Depreciation and Amortization of Property, Equipment and Software	26,600,000	21,700,000
Amortization of Intangibles Assets Acquired	14,100,000	24,300,000
Contribution to Defined Benefit Pension Plan	0	(55,300,000)
Loss from Early Extinguishment of Debt	0	5,800,000
Change in Accumulated Undistributed Earnings of Equity Method Limited Liability Investments	5,600,000	9,700,000
Decrease (Increase) in Value of Equity and Convertible Securities at Fair Value	1,000,000.0	(99,700,000)
Receivables from Policyholders	(132,200,000)	(132,800,000)
Reinsurance Recoverables	13,800,000	39,800,000
Deferred Policy Acquisition Costs	(40,500,000)	(66,500,000)
Insurance Reserves	(10,300,000)	71,500,000
Unearned Premiums	136,100,000	150,700,000
Income Taxes	22,000,000.0	46,100,000
Other Assets and Liabilities	(79,100,000)	(28,200,000)
Net Cash Provided by Operating Activities	251,300,000	366,500,000
Cash Flows from Investing Activities:
Proceeds from Sales, Calls and Maturities of Fixed Maturities	707,000,000.0	1,067,900,000
Proceeds from the Sales or Paydowns of Investments:
Equity Securities	436,500,000	99,700,000
Real Estate Investments	5,400,000	0
Mortgage Loans	18,600,000	0
Other Investments	26,500,000	25,700,000
Purchases of Investments:
Fixed Maturities	(1,009,700,000)	(1,013,700,000)
Equity Securities	(324,400,000)	(248,200,000)
Real Estate Investments	(500,000)	(1,200,000)
Corporate-owned Life Insurance	(100,000,000.0)	(50,000,000.0)
Mortgage Loans	(22,700,000)	0
Other Investments	(17,900,000)	(94,100,000)
Net Sales (Purchases) of Short-term Investments	(147,900,000)	(111,500,000)
Acquisition of Software and Long-lived Assets	(46,200,000)	(53,800,000)
Other	6,000,000.0	(2,000,000.0)
Net Cash Provided (Used In) by Investing Activities	(469,300,000)	(381,200,000)
Cash Flows from Financing Activities:
Net Proceeds from Issuance of Long-term Debt	395,600,000	49,900,000
Repayment of Long-term Debt	0	(185,000,000.0)
Proceeds from Policyholder Contract Liabilities	391,800,000	385,600,000
Repayment of Policyholder Contract Liabilities	(192,400,000)	(258,000,000.0)
Proceeds from Issuance of Common Stock, Net of Transaction Costs	0	127,500,000
Proceeds from Shares Issued under Employee Stock Purchase Plan	3,100,000	1,000,000.0
Common Stock Repurchases	(110,400,000)	0
Dividends and Dividend Equivalents Paid	(59,300,000)	(49,100,000)
Other	5,000,000.0	1,300,000
Net Cash Provided by Financing Activities	433,400,000	73,200,000
Increase in Cash	215,400,000	58,500,000
Cash, Beginning of Year	136,800,000	75,100,000
Cash, End of Period	$ 352,200,000	$ 133,600,000