Revenue Recognition - Summary of Revenue Disaggregated by Categories (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
May 31, 2026	May 31, 2025	May 31, 2026	May 31, 2025
Disaggregation of Revenue [Line Items]
Revenue	$ 576.5	$ 842.7	$ 1,870.1	$ 2,480.7
Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenue	529.1	793.4	1,727.6	2,337.2
Leasing and Fleet Management [Member]
Disaggregation of Revenue [Line Items]
Revenue	47.4	49.3	142.5	143.5
Rail Cars [Member] \| Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenue	431.7	694.3	1,454.9	2,045.2
Railcar Maintenance [Member] \| Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 97.4	$ 99.1	$ 272.7	$ 292.0

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.

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+ Details

- Definition

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.

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+ Details