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Goodwill and Other Intangible Assets - Rollforward of Goodwill and Indefinite Lived Assets (Details) - USD ($) | 12 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017
Goodwill [Roll Forward] |  |  |
Balance - 31 March 2018 | $ 4,900,000 |  |
Acquired during the period | 220,000,000 |  |
Impairment | (4,600,000) |  |
Foreign exchange impact | (19,200,000) |  |
Balance - 31 March 2019 | 201,100,000 | $ 4,900,000 |
Indefinite-lived Intangible Assets [Roll Forward] |  |  |
Balance - 31 March 2018 | 0 |  |
Acquired during the period | 126,800,000 |  |
Foreign exchange impact | (10,700,000) |  |
Balance - 31 March 2019 | 116,100,000 | 0 |
Other | 7,400,000 | 7,400,000 |
Europe Building Products |  |  |
Goodwill [Roll Forward] |  |  |
Balance - 31 March 2019 | 200,800,000 |  |
Asia Pacific |  |  |
Goodwill [Roll Forward] |  |  |
Balance - 31 March 2018 | 300,000 |  |
Balance - 31 March 2019 | 300,000 | 300,000 |
Other Businesses |  |  |
Goodwill [Roll Forward] |  |  |
Balance - 31 March 2018 | 4,600,000 |  |
Impairment | $ (4,600,000) | 0 | $ 0
Balance - 31 March 2019 |  | $ 4,600,000 |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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- Definition Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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- Definition Carrying amount (original costs adjusted for previously recognized amortization and impairment) as of the balance sheet date for the rights acquired through registration of a trade name to gain or protect exclusive use thereof for a projected indefinite period of benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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