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

Operating Segment Information and Concentrations of Risk - Summary of Gross Sales by Major Customers (Detail)

v2.4.0.8
Operating Segment Information and Concentrations of Risk - Summary of Gross Sales by Major Customers (Detail) (USA & Europe Fibre Cement [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Mar. 31, 2012
Segment Reporting Information [Line Items]      
Gross Sales of Major Customers $ 313.8 $ 360.7 $ 343.1
Customer A [Member]
      
Segment Reporting Information [Line Items]      
Gross Sales of Major Customers 174.2 223.0 207.4
Gross sales percentage 11.70% 16.90% 16.80%
Customer B [Member]
      
Segment Reporting Information [Line Items]      
Gross Sales of Major Customers $ 139.6 $ 137.7 $ 135.7
Gross sales percentage 9.30% 10.40% 11.00%