Shareholders' Equity (Reclassification out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (6.1)	$ (11.7)	$ (18.7)	$ (31.6)
Tax impact	(15.2)	(16.0)	50.9	(48.8)
Total (income) loss, net of tax	(54.0)	(73.2)	121.9	(166.8)
Total (income) loss from continuing operations, net of tax	(54.2)	(90.7)	118.9	(190.8)
Adjustments related to Sale to Knauf	6.2	(78.6)	8.2	(84.6)
Amounts reclassified from accumulated other comprehensive (loss)	(2.2)	87.0	275.4	92.1
Derivative Gain (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive (loss)	(1.5)	0.4	(2.9)	1.2
Pension And Postretirement Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive (loss)	(0.7)	5.4	278.3	9.7
Foreign Currency Translation Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive (loss)		81.2		81.2
Reclassification From Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(2.2)	87.0	275.4	92.1
Reclassification From Accumulated Other Comprehensive Loss [Member] | Derivative Gain (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Tax impact	0.4	(0.1)	0.8	(0.3)
Total (income) loss, net of tax	(1.5)	0.4	(2.9)	1.2
Reclassification From Accumulated Other Comprehensive Loss [Member] | Derivative Gain (Loss) [Member] | Interest Rate Swap Contracts, Before Tax [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(1.9)	0.5	(3.7)	1.5
Reclassification From Accumulated Other Comprehensive Loss [Member] | Prior Service Credit Amortization [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other non-operating (income) expense, net	(0.1)	(0.1)	(0.2)	(0.1)
Reclassification From Accumulated Other Comprehensive Loss [Member] | Amortization of Net Actuarial Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other non-operating (income) expense, net	(0.9)	2.7	0.5	8.0
Reclassification From Accumulated Other Comprehensive Loss [Member] | Settlement [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other non-operating (income) expense, net			374.4
Reclassification From Accumulated Other Comprehensive Loss [Member] | Pension And Postretirement Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total (income) loss, before tax	(1.0)	2.6	374.7	7.9
Income tax expense	0.3	(0.7)	(96.4)	(1.7)
Total (income) loss from continuing operations, net of tax	(0.7)	1.9	278.3	6.2
Adjustments related to Sale to Knauf		3.5		3.5
Total (income) loss, net of tax	$ (0.7)	5.4	$ 278.3	9.7
Reclassification From Accumulated Other Comprehensive Loss [Member] | Foreign Currency Translation Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive (loss)		$ 81.2		$ 81.2