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Reclassification from AOCI due to forecasted sales no longer probable of occurring.

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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- Definition

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.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount of gain (loss) on derivative instrument designated and qualifying as fair value hedge included in assessment of hedge effectiveness, recognized in earnings.

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

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, before tax and after adjustments, of gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge, attributable to parent. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Loss (Gain) Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
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 cashflow hedges are recorded	$ 208.4	$ 298.6	$ 719.5	$ 917.2
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of fair value hedges are recorded	12.9	12.3	39.1	36.3
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of fair value hedges are recorded	0.5	0.8	0.8	0.4
Cost of Sales \| Not Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	(1.5)		(0.1)
Cost of Sales \| Not Designated as Hedging Instrument \| Alloying metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income – Realized loss	0.3		1.7
Loss (gain) recognized in our Statements of Consolidated Income – Unrealized gain	(1.8)		(1.8)
Depreciation and Amortization \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Foreign exchange contracts			(0.1)
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 cashflow hedges are recorded	208.4	298.6	719.5	917.2
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	1.6	5.4	19.2	14.3
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument \| Electricity
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income			0.6
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument \| Aluminum
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	1.2	4.8	14.5	13.5
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument \| Natural Gas
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income	0.3	0.1	1.2	0.1
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income		0.5	2.1	0.7
Cash Flow Hedges \| Cost of Sales \| Designated as Hedging Instrument \| Alloying Metals (Reclassification Due To Forecasted Transactions No Longer Probable of Occurring
Derivative Instruments Gain Loss [Line Items]
Alloying metals (reclassification from AOCI due to forecasted transactions no longer probable of occurring)	0.1		0.8
Fair Value 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 fair value hedges are recorded	12.9	12.3	39.1	36.3
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of fair value hedges are recorded	$ (0.5)	$ (0.8)	(0.8)	$ (0.4)
Fair Value Hedges \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Income			0.3
Fair Value Hedges \| Depreciation and Amortization \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Hedged item			0.1
Excluded component amortized from AOCI			0.4
Fair Value Hedges \| Other Expense, Net \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Reclassification from AOCI related to early termination of firm commitment			(0.4)
Net settlement related to early termination of forward contracts			$ 0.3