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Property, Plant and Equipment - Summary of Impairment Charges (Details) - USD ($) $ in Millions | 12 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |
Impairment of Property, Plant & Equipment | $ 64.5 | $ 9.1 | $ 0.7
North America Fiber Cement |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |
Impairment of Property, Plant & Equipment | 44.0 | 3.0 | 0.7
Asia Pacific Fiber Cement |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |
Impairment of Property, Plant & Equipment | 15.0 | 0.0 | 0.0
Europe Building Products |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |
Impairment of Property, Plant & Equipment | 5.5 | 0.0 | 0.0
Other Businesses |  |  |
Impaired Long-Lived Assets Held and Used [Line Items] |  |  |
Impairment of Property, Plant & Equipment | $ 0.0 | $ 6.1 | $ 0.0

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