Discontinued Operations (Summary of Total Estimated Gains and Losses, Capital Expenditures and Operating Lease) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business	$ (5.0)	$ 2.2
Right-of-use assets obtained in exchange for lease obligations	0.6	29.2
EMEA and Pacific Rim Business [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business	(5.0)	2.2
Purchases of property, plant and equipment		(0.4)
Operating lease cost		2.3
Right-of-use assets obtained in exchange for lease obligations		24.6
EMEA and Pacific Rim Business [Member] | Knauf [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business	$ 5.0	$ (2.2)