Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Amortized cost of fixed maturities	$ 7,811.8	$ 7,358.2
Allowance for credit losses	(9.6)	(7.5)	$ (3.3)
Cost of equity securities	247.6	618.7
Premium Receivable, Allowance for Credit Loss	13.1	13.6	$ 20.9
Long-term Debt	$ 1,195.1	$ 1,152.1
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares outstanding (in shares)	63,912,762	63,684,628