Segment Information - Profit or loss information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 13,835.0	$ 14,805.9	$ 17,025.0
Less:
Cost of sales (exclusive of depreciation and amortization shown below)	9,728.4	10,258.6	11,773.7
Depreciation and amortization expense	268.7	245.4	240.2
Impairment	11.7
Interest expense	40.3	40.1	62.3
Income tax provision	261.9	400.6	586.2
Net income	878.0	1,340.1	1,844.2
Other Segment Disclosures
Purchases of property, plant and equipment	430.6	468.8	341.8
Metals Service Centers
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	13,835.0	14,805.9	17,025.0
Less:
Net income	878.0	1,340.1	1,844.2
Other Segment Disclosures
Purchases of property, plant and equipment	430.6	468.8	341.8
Metals Service Centers | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	13,835.0	14,805.9	17,025.0
Less:
Cost of sales (exclusive of depreciation and amortization shown below)	9,728.4	10,258.6	11,773.7
Compensation expense	1,614.8	1,557.8	1,537.3
Other segment items	1,031.2	963.3	981.1
Depreciation and amortization expense	268.7	245.4	240.2
Impairment	11.7
Interest expense	40.3	40.1	62.3
Income tax provision	261.9	400.6	586.2
Net income	$ 878.0	$ 1,340.1	$ 1,844.2