Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Amortized cost of fixed maturities	$ 6,692,700,000	$ 6,372,700,000
Cost of equity securities	684,100,000	818,800,000
Receivables from Policyholders, allowance for credit losses	20,900,000	22,300,000
Debt	$ 1,247,800,000	$ 820,200,000
Common stock, par value (in dollars per share)	$ 0.10
Common stock, shares authorized (in shares)	100,000,000
Common stock, shares outstanding (in shares)	65,436,207	66,665,888
Amortized cost of fixed maturities	$ (3,300,000)	$ 0