Shareholders' Equity (Schedule of Accumulated Other Comprehensive (Loss) Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 450.9	$ 364.9
Impact of ASU 2017-12 adoption	895.0		$ 869.8
Other comprehensive (loss) income before reclassifications, net of tax benefit (expense)	5.9	(5.1)
Amounts reclassified from accumulated other comprehensive (loss)	(1.3)	279.5
Net current period other comprehensive (loss) income	4.6	274.4
Balance	473.6	370.4
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	2.3	9.4
Other comprehensive (loss) income before reclassifications, net of tax benefit (expense)	0.6	(2.1)
Net current period other comprehensive (loss) income	0.6	(2.1)
Balance	2.9	7.3
Derivative Gain (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(19.0)	(8.5)
Other comprehensive (loss) income before reclassifications, net of tax benefit (expense)	5.3	(11.6)
Amounts reclassified from accumulated other comprehensive (loss)	(1.5)	(0.2)
Net current period other comprehensive (loss) income	3.8	(11.8)
Balance	(15.2)	(20.3)
Pension And Postretirement Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(92.6)	(377.0)
Other comprehensive (loss) income before reclassifications, net of tax benefit (expense)		8.6
Amounts reclassified from accumulated other comprehensive (loss)	0.2	279.7
Net current period other comprehensive (loss) income	0.2	288.3
Balance	(92.4)	(88.7)
Accumulated Other Comprehensive (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(109.3)	(376.1)
Balance	$ (104.7)	$ (101.7)