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v3.19.1

Property, Plant and Equipment - Components of Property, Plant and Equipment 2 (Detail) - USD ($) $ in Millions | 12 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017
Property, Plant and Equipment [Line Items] |  |  |
Capitalized interest | $ 5.4 | $ 4.8 | $ 2.0
Net book value of disposals | 28.0 | 16.4 |
Net book value of disposals, usage of replacement parts | 13.7 | 13.9 |
Impairment of Long-Lived Assets to be Disposed of | 9.1 | 0.7 | 0.5
Net book value of disposals, disposal of assets no longer in use | 5.2 | 1.8 |
Held-for-sale [Member] | Buildings |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Buildings held for sale | 5.8 |  |
Cost of Sales [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment of Long-Lived Assets to be Disposed of | 0.4 | $ 0.7 | $ 0.5
North America Fiber Cement |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment of Long-Lived Assets to be Disposed of | 6.1 |  |
Other Businesses |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment of Long-Lived Assets to be Disposed of | $ 2.6 |  |

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