Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Oct. 31, 2015 |
Oct. 31, 2014 |
Oct. 31, 2015 |
Oct. 31, 2014 |
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| Accumulated Other Comprehensive Income (Loss) [Line Items] | ||||
| Tax effects on reclassifications of realized net losses | $ 0.3 | $ 0.3 | $ 0.6 | $ 0.6 |
| X | ||||||||||
- 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. No definition available.
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| X | ||||||||||
- Definition Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans. No definition available.
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