Restructuring, net - Narrative (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
Proceeds from sale of property, plant and equipment	108.2	0.4	4.2
General Corporate and R&D
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(24.2)	0.0	20.1
Gain on sale of assets	26.2
Asset impairment charges	2.0
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

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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