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Financial Instruments - Financial Instruments and Balance Sheet Classification (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Jul. 31, 2022 | Jul. 31, 2021 | Apr. 30, 2022
Investments Debt And Equity Securities [Abstract] |  |  |
Obligations for which assets are held in trust | $ 178.8 |  | $ 160.8
Gain on marketable securities | 0.1 | $ 5.2 |
Unvested obligations under deferred compensation plans | $ 17.5 |  | $ 24.0

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