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Property, Plant and Equipment - Components of Property, Plant and Equipment 2 (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018
Property, Plant and Equipment [Line Items] |  |  |
Capitalized interest | $ 9.5 | $ 5.4 | $ 4.8
Operating lease right-of-use-assets | 40.5 | 0.0 |
Net book value of disposals | 15.0 | 28.0 |
Net book value of disposals, usage of replacement parts | 11.7 | 13.7 |
Net book value of disposals, disposal of assets no longer in use | 3.3 | 5.2 |
Held-for-sale |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Buildings held for sale |  | 5.8 |
Cost of Sales |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment of long-lived assets |  | 0.4 |
North America Fiber Cement |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Operating lease right-of-use-assets | $ (0.8) |  |
Impairment of long-lived assets |  | 2.6 |
Other Businesses |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment of long-lived assets |  | $ 6.1 |

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