Acquisitions and Discontinued Operations (Narrative) (Details) $ in Millions			1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 13, 2017 USD ($)	Apr. 01, 2016	Apr. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 04, 2014 USD ($)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Business acquisition, goodwill				$ 11.3	$ 11.3	$ 0.5
Separation costs						34.5	$ 34.3
EMEA and Pacific Rim Business [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Asset impairment charges				74.0
EMEA and Pacific Rim Business [Member] | Foreign Currency Translation Adjustments [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Accumulated other comprehensive income adjustments				$ 51.4
Flooring Businesses [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Common stock split ratio of AFI share to AWI shares		0.5
Separation costs						34.5	$ 34.3
Initial term of campus lease agreement period					5 years
DLW [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Contingent liability								$ 12.9
Assets removed from balance sheet								151.9
Liabilities removed from balance sheet								$ 164.8
Settlement agreement and mutual release with administrator to settle all claims of Administrator related to insolvency for a cash payment			$ 11.8
DLW [Member] | Accounts Payable and Accrued Expenses [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Contingent liability						$ 11.9
Tectum [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Business acquisition, purchase price	$ 31.2
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed	4.4
Business acquisition, total fair value of intangible assets of amortizable customer relationships and non-amortizing brand names	16.0
Business acquisition, goodwill	$ 10.8