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Acquisitions and Dispositions - Dispositions (Details) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2024 service_center_store	Sep. 30, 2024 USD ($) service_center_store	Dec. 31, 2024 service_center_store	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of business				$ 71.1	$ 41.8	$ 0.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of service center stores sold \| service_center_store	39	28	67
Gain (loss) on disposition of business				73.9	41.8
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued operations				$ 0.0	0.0	1,571.6
Discontinued Operations, Held-for-sale \| Former Global Products Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal of discontinued operations						$ (8.1)
Current liabilities held for sale		$ 3.9			$ 3.9