Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Goodwill and Other Intangible Assets - Rollforward of Finite-Lived Assets (Details)

v3.19.1
Goodwill and Other Intangible Assets - Rollforward of Finite-Lived Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2017
Finite-lived Intangible Assets [Roll Forward]      
Amortization $ (6.1) $ (0.9) $ (0.8)
Impairment (2.6) 0.0 $ 0.0
Other intangible assets [Member]      
Finite-lived Intangible Assets [Roll Forward]      
Balance - 31 March 2018 9.7    
Beginning Balance, Accumulated Amortization (4.8)    
Beginning Balance, Net 4.9    
Acquired during the period 2.4    
Amortization (1.3)    
Impairment (2.6)    
Foreign exchange impact (0.3)    
Foreign exchange impact 0.1    
Foreign exchange impact (0.2)    
Ending Balance, Net 3.2 4.9  
Ending Balance, Accumulated Amortization (8.6) (4.8)  
Ending Balance, Gross 11.8 9.7  
Customer relationships [Member]      
Finite-lived Intangible Assets [Roll Forward]      
Balance - 31 March 2018 0.0    
Beginning Balance, Accumulated Amortization 0.0    
Beginning Balance, Net 0.0    
Acquired during the period 57.8    
Amortization (4.8)    
Foreign exchange impact (5.8)    
Foreign exchange impact 0.5    
Foreign exchange impact (5.3)    
Ending Balance, Net 47.7 0.0  
Ending Balance, Accumulated Amortization (4.3) 0.0  
Ending Balance, Gross 52.0 $ 0.0  
Other Businesses      
Finite-lived Intangible Assets [Roll Forward]      
Impairment (2.2)    
North America Fiber Cement      
Finite-lived Intangible Assets [Roll Forward]      
Impairment $ (0.4)