Derivatives, Hedging Programs and Other Financial Instruments - Summary of Loss (Gain) Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
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	$ 731.1	$ 865.9
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
Not Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	$ (0.1)	$ (1.6)
Not Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		(0.6)
Loss (gain) recognized in our Statements of Consolidated Income Unrealized gain	(0.1)	(1.0)
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	731.1	865.9
Cash Flow Hedges \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	0.2	(19.9)
Cash Flow Hedges \| Designated as Hedging Instrument \| Electricity
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		(0.3)
Cash Flow Hedges \| Designated as Hedging Instrument \| Natural Gas
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	(0.3)	(0.9)
Cash Flow Hedges \| Designated as Hedging Instrument \| Aluminum
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	$ 0.5	$ (18.7)

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a),(d))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

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