Derivatives, Hedging Programs and Other Financial Instruments - Summary of (Gain) Loss Associated with Derivative Contracts (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded		$ 673.4	$ 651.3	[1]
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded	Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded
Cash Flow Hedges
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded		$ 673.4	$ 651.3	[2]
Cash Flow Hedges | Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		(5.5)	2.1	[2]
Cash Flow Hedges | Designated as Hedging Instrument | Aluminum
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		(5.2)	2.0	[2]
Cash Flow Hedges | Designated as Hedging Instrument | Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		(0.4)
Cash Flow Hedges | Designated as Hedging Instrument | Foreign exchange contracts
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		$ 0.1
Cash Flow Hedges | Designated as Hedging Instrument | Natural Gas
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	[2]		0.3
Cash Flow Hedges | Designated as Hedging Instrument | Electricity
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	[2]		$ (0.2)

[1] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 14 for further discussion.

[2] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 14 for further discussion.