Pension Benefits, Other Postretirement Benefits and Employee Savings and Investment Plans (Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Assets & Liabilities:
Non-current assets	$ 5.3	$ 5.2
Current liabilities	0.0	0.0
Non-current liabilities	0.0	(0.2)
Net assets (liabilities)	5.3	5.0
Accumulated Other Comprehensive Loss:
Net actuarial (loss) gain	(11.6)	(11.8)
Accumulated other comprehensive (loss) income	(11.6)	(11.8)
Other Postretirement Benefits
Assets & Liabilities:
Non-current assets	0.0	0.0
Current liabilities	(0.2)	(0.2)
Non-current liabilities	(1.4)	(1.2)
Net assets (liabilities)	(1.6)	(1.4)
Accumulated Other Comprehensive Loss:
Net actuarial (loss) gain	0.2	0.2
Accumulated other comprehensive (loss) income	$ 0.2	$ 0.2