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

Operating Segment Information and Concentrations of Risk - Summary of Operating Segments (Detail)

v3.8.0.1
Operating Segment Information and Concentrations of Risk - Summary of Operating Segments (Detail) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Segment Reporting Information [Line Items]      
Net sales $ 2,054.5 $ 1,921.6 $ 1,728.2
Total operating income 229.2 393.2 354.0
Net interest expense (29.5) (27.5) (25.6)
Loss on early debt extinguishment (26.1) 0.0 0.0
Other income 0.7 1.3 2.1
Income before income taxes 174.3 367.0 330.5
Total Identifiable Assets 2,351.0 2,012.7  
Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Total operating income 453.9 406.8 397.6
Total Identifiable Assets 1,459.9 1,293.8  
General Corporate [Member]      
Segment Reporting Information [Line Items]      
Total operating income (224.7) (13.6) (43.6)
Total Identifiable Assets 891.1 718.9  
North America Fiber Cement [Member]      
Segment Reporting Information [Line Items]      
Net sales 1,578.1 1,493.4 1,335.0
North America Fiber Cement [Member] | Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Total operating income 381.9 343.9 352.2
Total Identifiable Assets 1,070.7 917.4  
International Fiber Cement [Member]      
Segment Reporting Information [Line Items]      
Net sales 461.7 411.8 379.4
International Fiber Cement [Member] | Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Total operating income 108.4 95.1 77.9
Total Identifiable Assets 351.6 335.7  
Other Businesses [Member]      
Segment Reporting Information [Line Items]      
Net sales 14.7 16.4 13.8
Other Businesses [Member] | Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Total operating income (8.6) (6.7) (8.6)
Total Identifiable Assets 30.1 28.4  
Research and Development [Member] | Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Total operating income (27.8) (25.5) $ (23.9)
Total Identifiable Assets $ 7.5 $ 12.3