Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Millions	12 Months Ended
May 31, 2024	May 31, 2023	May 31, 2022
Disaggregation Of Revenue [Line Items]
Net sales	$ 3,430.6	$ 3,607.7	$ 4,068.9
Direct \| Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	3,269.4	3,464.9	3,923.1
Toll \| Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	$ 161.2	$ 142.8	$ 145.8

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.

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Topic 280
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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+ Details