Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Net AWI Investments (Details)

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Summary of Significant Accounting Policies - Net AWI Investments (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Apr. 01, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Consolidated Statements of Stockholders' Equity          
Net transfers (to) from AWI during period $ (11.2) $ 53.6 $ (0.8) $ 42.4 $ 5.1
Other activity concurrent with Spin-off 0.0        
Cash distribution paid to AWI upon Spin-off (50.0)     (50.0)  
Net transfers (to) from AWI       (7.6)  
Consolidated Statements of Cash Flows - Financing Activities          
Net transfers (to) from AWI 9.0 $ 53.6 0.0 55.6 5.3
Other activity concurrent with Spin-off (7.0)        
Cash distribution paid to AWI upon Spin-off $ (50.0)   $ 0.0 (50.0) $ 0.0
Net transfers (to) from AWI       $ 5.6