Investment in Unconsolidated Affiliate - Schedule of Financial Information of Unconsolidated Affiliates (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Nov. 30, 2024	Aug. 31, 2024	Nov. 30, 2023	Aug. 31, 2023	Nov. 30, 2024	Nov. 30, 2023	May 31, 2024
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	$ 52.0				$ 52.0		$ 40.2
Total assets	1,739.3				1,739.3		1,866.4
Current liabilities	467.7				467.7		618.4
Other noncurrent liabilities	35.3				35.3		34.3
Equity	1,010.8				1,010.8		985.3
Total liabilities and equity	1,739.3				1,739.3		1,866.4
Net sales	739.0		$ 808.0		1,573.0	$ 1,713.8
Gross margin	80.0		60.2		180.4	188.7
Operating income	18.9		(8.8)		62.3	60.9
Depreciation and amortization					32.5	33.3
Income tax expense	3.6		(2.5)		7.6	14.5
Net earnings (loss)	16.1	$ 32.2	(2.1)	$ 62.1	48.3	60.0
Serviacero Worthington
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	20.8				20.8		5.7
Other current assets	249.3				249.3		274.7
Noncurrent assets	58.4				58.4		58.3
Total assets	328.5				328.5		338.7
Current liabilities	53.7				53.7		64.7
Other noncurrent liabilities	5.1				5.1		5.2
Equity	269.7				269.7		268.8
Total liabilities and equity	328.5				328.5		$ 338.7
Net sales	138.7		163.4		287.2	315.3
Gross margin	9.6		18.6		25.2	39.9
Operating income	5.5		15.2		17.2	33.1
Depreciation and amortization	1.2		1.1		2.3	2.1
Interest expense	0.0		0.0		0.0	0.0
Income tax expense	5.8		6.3		12.6	7.0
Net earnings (loss)	$ (1.7)		$ 7.6		$ 0.9	$ 25.5