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Dividends - Summary of Dividends Paid (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019
Dividends Payable [Line Items] |  |  |
Dividends | $ 0.0 | $ 158.6 | $ 172.1
FY 2021 special dividend |  |  |
Dividends Payable [Line Items] |  |  |
Interim ordinary dividend to shareholders (in dollars per share) | $ 0.70 |  |
Dividends | $ 309.6 |  |
FY 2020 first half dividend |  |  |
Dividends Payable [Line Items] |  |  |
Interim ordinary dividend to shareholders (in dollars per share) | $ 0.10 |  |
Dividends | $ 44.7 |  |
FY 2019 second half dividend |  |  |
Dividends Payable [Line Items] |  |  |
Interim ordinary dividend to shareholders (in dollars per share) | $ 0.26 |  |
Dividends | $ 113.9 |  |
FY 2019 first half dividend |  |  |
Dividends Payable [Line Items] |  |  |
Interim ordinary dividend to shareholders (in dollars per share) | $ 0.10 |  |
Dividends | $ 43.6 |  |
FY 2018 second half dividend |  |  |
Dividends Payable [Line Items] |  |  |
Interim ordinary dividend to shareholders (in dollars per share) | $ 0.30 |  |
Dividends | $ 128.5 |  |

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- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585 + Details
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