Discontinued Operations (Summary of Total Estimated Gains and Losses, Capital Expenditures and Operating Lease) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business		$ (6.8)	$ (4.2)	$ (4.6)
Right-of-use assets obtained in exchange for lease obligations			1.1	35.6
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		$ (6.8)	(5.0)	(4.6)
Purchases of property, plant and equipment				(1.4)
Operating lease cost				4.9
Right-of-use assets obtained in exchange for lease obligations				24.6
European Resilient Flooring [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain on dissolution of flooring entity (3)	$ (0.8)		(0.8)
Knauf [Member] | EMEA and Pacific Rim Business [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Loss on sale to Knauf (1)			$ 5.0
Gain (loss) on disposal of discontinued business				$ 4.6