Pensions and Postretirement Benefits Other Than Pensions (Schedule of Pretax Amounts Recognized in Accumulated Other Comprehensive Income (Loss) Other Than Pension) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current year changes recorded to Accumulated other comprehensive income (loss)	$ 16.8	$ 54.2	$ 111.4
Pension and OPEB adjustments amortization reclassified to earnings	(7.4)	(21.6)	(38.6)
Stockholders' Equity Note, Spinoff Transaction		(18.9)	$ (49.0)
Other Postretirement Benefits Plan [Member]
Balance at December 31, 2013	117.2
Current year changes recorded to Accumulated other comprehensive income (loss)	7.4
Pension and OPEB adjustments amortization reclassified to earnings	(12.4)
Balance at December 31, 2014	112.2	117.2
Net Actuarial Losses [Member] | Other Postretirement Benefits Plan [Member]
Balance at December 31, 2013	120.5
Current year changes recorded to Accumulated other comprehensive income (loss)	7.4
Pension and OPEB adjustments amortization reclassified to earnings	(13.0)
Balance at December 31, 2014	114.9	120.5
Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Balance at December 31, 2013	(3.3)
Current year changes recorded to Accumulated other comprehensive income (loss)	0.0
Pension and OPEB adjustments amortization reclassified to earnings	0.6
Balance at December 31, 2014	$ (2.7)	$ (3.3)