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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
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- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

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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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) MWh Contract kt	Mar. 31, 2020 USD ($)	Dec. 31, 2020 MWh 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	$ (52)	$ (25)
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		(14)
Energy Contracts [Member] \| Other Comprehensive Loss [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Forecasted energy purchases in megawatt hours \| MWh	821,304		1,427,184
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	2,074		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	$ (145)
Derivatives Designated as Hedging Instruments [Member] \| Financial Contracts [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	$ (14)
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		(7)
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 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