Aluminum forecasted sales designated as fair value hedges in kilo metric ton.

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- Definition

Number of new financial contracts.

+ References

No definition available.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) kt	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) kt	Sep. 30, 2020 USD ($)	Mar. 31, 2021 Contract	Dec. 31, 2020 kt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings	$ (82)	$ (29)	$ (201)	$ (67)
Level 1 and 2 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings	$ (4)	(2)	(7)	(17)
Derivatives Designated as Hedging Instruments [Member] \| Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings			$ (7)
Derivatives Designated as Hedging Instruments [Member] \| Level 1 and 2 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings				(17)
Derivatives Designated as Hedging Instruments [Member] \| Power Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aluminum forecast sales \| kt	1,962		1,962			2,130
Derivatives Designated as Hedging Instruments [Member] \| Power Contract [Member] \| Cash Flow Hedging [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amount of (loss) gain expected to be recognized into earnings over the next 12 months			$ (273)
Derivatives Designated as Hedging Instruments [Member] \| Sales [Member] \| Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings	$ (4)		(6)
Derivatives Designated as Hedging Instruments [Member] \| Sales [Member] \| Level 1 and 2 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings				(7)
Derivatives Designated as Hedging Instruments [Member] \| Cost of Goods Sold [Member] \| Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings			$ (1)
Derivatives Designated as Hedging Instruments [Member] \| Cost of Goods Sold [Member] \| Level 1 and 2 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive (loss) income to earnings		$ (2)		$ (10)
Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of new financial contracts \| Contract					4