Annual and transition report of foreign private issuers [Sections 13 or 15(d)]

Revenues (Details)

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Revenues (Details) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Disaggregation of Revenue [Line Items]      
Total $ 3,877.5 $ 3,936.3 $ 3,777.1
Fiber cement      
Disaggregation of Revenue [Line Items]      
Total 3,467.5 3,531.2 3,395.4
Fiber gypsum      
Disaggregation of Revenue [Line Items]      
Total 410.0 405.1 381.7
North America Fiber Cement      
Disaggregation of Revenue [Line Items]      
Total 2,863.3 2,891.4 2,787.6
North America Fiber Cement | Fiber cement      
Disaggregation of Revenue [Line Items]      
Total 2,863.3 2,891.4 2,787.6
North America Fiber Cement | Fiber gypsum      
Disaggregation of Revenue [Line Items]      
Total 0.0 0.0 0.0
Asia Pacific Fiber Cement      
Disaggregation of Revenue [Line Items]      
Total 519.9 562.8 539.2
Asia Pacific Fiber Cement | Fiber cement      
Disaggregation of Revenue [Line Items]      
Total 519.9 562.8 539.2
Asia Pacific Fiber Cement | Fiber gypsum      
Disaggregation of Revenue [Line Items]      
Total 0.0 0.0 0.0
Europe Building Products      
Disaggregation of Revenue [Line Items]      
Total 494.3 482.1 450.3
Europe Building Products | Fiber cement      
Disaggregation of Revenue [Line Items]      
Total 84.3 77.0 68.6
Europe Building Products | Fiber gypsum      
Disaggregation of Revenue [Line Items]      
Total $ 410.0 $ 405.1 $ 381.7