Restructuring, net - Schedule of Restructuring and Related Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 16.2	$ 50.3	$ 20.1
General Corporate and R&D
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(24.2)	0.0	20.1
Australia & New Zealand \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1.4	50.3	0.0
Siding & Trim \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	35.6	0.0	0.0
Deck, Rail & Accessories \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	3.4	0.0	0.0
Equipment write-offs, including disposal costs \| Australia & New Zealand \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0.0	30.3	0.0
Equipment write-offs, including disposal costs \| Siding & Trim \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	22.1	0.0	0.0
Reclassification of foreign currency translation adjustments \| Australia & New Zealand \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1.4	8.3	0.0
Other exit costs \| Australia & New Zealand \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0.0	11.7	0.0
Other exit costs \| Siding & Trim \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 13.5	$ 0.0	$ 0.0