Pension Plans (Schedule of Fair Values of Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	$ 7,481.8	$ 7,723.9
Equity securities	241.9	661.3
Investments Net Asset Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	284.7	354.0
Equity securities	37.6	52.3
Total investment assets at fair value	$ 322.3	$ 406.3