Financial Instruments and Risk Management (Schedule of Available-for-sale Securities Reconciliation) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Cost	$ 37.8	$ 38.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.8)	(2.7)
Fair Value	37.0	35.3
Available-for-sale fixed income investments
Debt Securities, Available-for-sale [Line Items]
Cost	37.8	38.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.8)	(2.7)
Fair Value	$ 37.0	$ 35.3