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

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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

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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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).

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Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) MWh kt	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) MWh kt	Jun. 30, 2019 USD ($)	Dec. 31, 2019 MWh kt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) cash flow hedges	$ (13)	$ (10)	$ (38)	$ (1)
Level 3 [Member] \| Financial Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial contract assets, fair value	7		7
Level 1 and 2 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) cash flow hedges	$ (1)	(8)	$ (15)	(12)
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	2,265,872		2,265,872		3,891,096
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 gain (loss) cash flow hedges			$ (15)
Derivatives Designated as Hedging Instruments [Member] \| Power Related Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aluminum forecast sales \| kt	2,244		2,244		2,347
Derivatives Designated as Hedging Instruments [Member] \| Power Related Derivative [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			$ (11)
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			4
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 gain (loss) cash flow hedges	$ (1)		(8)
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 gain (loss) cash flow hedges		$ (8)	$ (7)	$ (12)