Discontinued Operations (Summary of Total Gains and Losses, Capital Expenditures and Operating Lease) (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued business				$ (27.3)	$ (4.4)	$ (31.9)
Right-of-use assets obtained in exchange for lease obligations	[1]				4.1	39.4
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		$ (0.2)		$ (27.3)	(5.2)	(31.9)
Purchases of property, plant and equipment						(3.0)
Operating lease cost						7.4
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)					$ 5.2
Gain (loss) on disposal of discontinued business						$ 31.9

[1] The nine months ended September 30, 2019 includes initial ROU assets of $29.2 million recognized upon adoption on January 1, 2019