Investment in Unconsolidated Affiliate - Schedule of Financial Information of Unconsolidated Affiliates (Detail) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Feb. 29, 2024	Nov. 30, 2023	Aug. 31, 2023	Feb. 28, 2023	Nov. 30, 2022	Aug. 31, 2022	Feb. 29, 2024	Feb. 28, 2023	May 31, 2023
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	$ 60.8						$ 60.8		$ 32.7
Total assets	1,849.0						1,849.0		1,764.4
Current liabilities	645.4						645.4		478.4
Short-term borrowings	147.2						147.2		2.8
Current maturities of long-term debt	0.0						0.0		20.0
Other noncurrent liabilities	38.2						38.2		33.6
Equity	937.6						937.6		1,029.0
Total liabilities and equity	1,849.0						1,849.0		1,764.4
Net sales	805.8			$ 780.7			2,519.6	$ 2,723.7
Gross margin	120.1			63.2			308.8	186.3
Operating income (loss)	66.3			9.5			127.2	30.5
Depreciation and amortization	15.9			17.0			49.2	52.4
Income tax expense (benefit)	14.0			0.8			28.5	5.6
Net earnings (loss)	52.4	$ (2.1)	$ 62.1	9.3	$ (12.5)	$ 31.3	112.4	28.1
Serviacero Worthington
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	10.9						10.9		12.2
Other current assets	259.3						259.3		238.2
Noncurrent assets	58.1						58.1		58.9
Total assets	328.3						328.3		309.3
Current liabilities	63.5						63.5		70.8
Other noncurrent liabilities	5.3						5.3		5.4
Equity	259.5						259.5		233.1
Total liabilities and equity	328.3						328.3		$ 309.3
Net sales	137.3			114.9			452.6	434.9
Gross margin	10.8			(4.3)			50.7	11.7
Operating income (loss)	7.4			(7.2)			40.5	3.3
Depreciation and amortization	1.1			1.1			3.2	3.3
Interest expense	0.0			0.2			0.0	0.3
Income tax expense (benefit)	0.3			(4.6)			7.3	(2.0)
Net earnings (loss)	$ 5.8			$ (0.4)			$ 31.3	$ 7.0