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Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jan. 31, 2017 | Jan. 31, 2016 | Jan. 31, 2017 | Jan. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |
Tax effect on reclassifications of realized net losses | $ 0.3 | $ 0.3 | $ 0.9 | $ 0.9

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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 tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans. + References No definition available. + Details
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