Segment Information - Profit or loss information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 3,659.8	$ 3,643.3	$ 7,144.5	$ 7,288.1
Cost of sales (exclusive of depreciation and amortization shown below)	2,571.9	2,557.3	5,023.3	5,073.9
Depreciation and amortization expense	69.7	66.6	138.4	130.2
Interest expense	14.3	9.7	25.8	19.4
Income tax provision	70.1	81.4	132.0	173.8
Net income	234.2	268.3	434.7	572.1
Other Segment Disclosures
Purchases of property, plant and equipment			174.5	206.9
Metals Service Centers
Other Segment Disclosures
Purchases of property, plant and equipment	87.6	98.2	174.5	206.9
Metals Service Centers | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	3,659.8	3,643.3	7,144.5	7,288.1
Cost of sales (exclusive of depreciation and amortization shown below)	2,571.9	2,557.3	5,023.3	5,073.9
Compensation expense	434.6	403.2	854.7	817.0
Other segment items	265.0	256.8	535.6	501.7
Depreciation and amortization expense	69.7	66.6	138.4	130.2
Interest expense	14.3	9.7	25.8	19.4
Income tax provision	70.1	81.4	132.0	173.8
Net income	$ 234.2	$ 268.3	$ 434.7	$ 572.1