Acquisition and Discontinued Operations (Summary of Total Depreciation and Amortization, Capital Expenditures and Estimated Losses) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business, net of tax	$ 7.0		$ 5.9		$ (16.1)	$ 5.3
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, net of tax	2.4	$ (74.0)		$ (23.4)	(21.0)
Purchases of property, plant and equipment	(1.3)		(1.6)		(4.5)	(8.4)
Depreciation and amortization			$ 5.7			$ 16.5
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, net of tax	$ (2.4)				$ 21.0