Acquisitions and Discontinued Operations (Summary of Total Depreciation and Amortization and Capital Expenditures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Depreciation and amortization		$ 22.2	$ 34.4
Gain (loss) on disposal of discontinued business, net of tax	$ (13.3)	(70.0)	15.3
Purchases of property, plant and equipment	(7.3)	(12.0)	(37.9)
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	19.3	74.0
EMEA and Pacific Rim Business [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Depreciation and amortization		22.2	23.0
Gain (loss) on disposal of discontinued business, net of tax	(19.3)	(74.0)
Purchases of property, plant and equipment	(7.3)	(12.0)	(25.8)
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	19.3	74.0
Flooring Businesses [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Depreciation and amortization			11.4
Gain (loss) on disposal of discontinued business, net of tax	$ 6.0	$ 4.0	15.3
Purchases of property, plant and equipment			$ (12.1)