Derivatives and Other Financial Instruments - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($)	Apr. 30, 2016 Refinery	Dec. 31, 2018 USD ($) MWh Refinery Member Smelter Derivative kt	Dec. 31, 2017 USD ($) MWh kt	Dec. 31, 2016 USD ($) MWh
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Minimum members required for strategic risk management committee | Member			3
Unrealized gain (loss) recognized			$ (11,000,000)	$ 88,000,000
Number of alumina refineries to be powered under supplied agreement | Refinery		3
Other derivative contracts estimated term of quoted market prices, in years			10 years
Recognized an unrealized gain (loss)			$ 62,000,000	25,000,000
Derivatives Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			1
Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			1
London Metal Exchange [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			2
LME Plus Midwest Premium [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			3
Derivative One Through Derivative Five
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			5
Management estimates premium for next twelve months for number of contracts | Derivative			3
Minimum considerable period of significant change would result higher or lower fair value			10 years
Derivative D7 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of commodities interrelationship considered for embedded derivative valuation | Derivative			2
Embedded Credit Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative contract period			10 years
Derivative contract period, description			As Alcoa Corporation does not have outstanding 30-year debt, the Company’s estimated 30-year debt yield is represented by the sum of (i) the excess of the yield on Alcoa’s outstanding notes due 2026 over the yield on only the Ba/BB-rated company debt included in Barclays High Yield Index for intermediate (10-year) credits and (ii) the yield on only the Ba/BB-rated company debt included in Barclays High Yield Index for long (30-year) credits. In accordance with the terms of the power contract, this calculation may be changed in January of each calendar year.
Embedded Credit Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments			$ 4,000,000	3,000,000	$ (5,000,000)
Embedded Credit Derivative [Member] | Negotiated multiplier [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative contract period			30 years
Energy Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Increase (decrease) in derivative asset					(84,000,000)
Energy Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other income					7,000,000
Cost of goods sold					(6,000,000)
Energy Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost of goods sold				$ 6,000,000
Embedded Aluminum Derivative [Member] | Derivatives Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aluminum forecast sales | kt			2,508	2,859
Embedded Aluminum Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments			$ 19,000,000	$ (18,000,000)	(15,000,000)
Financial Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Recognized an unrealized gain (loss)					96,000,000
Financial Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments ineffectiveness					3,000,000
Net gain (loss) of derivative instruments				(7,000,000)	$ 3,000,000
Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of derivative contracts recorded as assets			2,000,000	44,000,000
Fair value of derivative contracts recorded as liabilities			$ 54,000,000	117,000,000
Derivative D11 [Member] | Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Forecasted energy purchases in megawatt hours | MWh					1,969,544
Electricity purchases			In addition, in January 2017, Alcoa Corporation entered into a new financial contract that hedges the anticipated power requirements at this smelter for the period from August 2017 through July 2021 (see D11 above). At December 31, 2018 and 2017, this financial contract hedges forecasted electricity purchases of 6,348,276 and 8,805,456, respectively, megawatt hours.
Derivative D11 [Member] | Energy Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost of goods sold			$ 70,000,000
Other Expenses (Income) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss)				22,000,000	$ 1,000,000
Other Expenses (Income), Net [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments			$ 23,000,000	$ (22,000,000)	(17,000,000)
Other Comprehensive Loss [Member] | Derivative D11 [Member] | Energy Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Forecasted energy purchases in megawatt hours | MWh			6,348,276	8,805,456
Cash Flow Hedging [Member] | Embedded Aluminum Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) on derivatives			$ (100,000,000)	$ (113,000,000)	(7,000,000)
Recognized an unrealized gain (loss)			785,000,000	(1,521,000,000)	(615,000,000)
Cash Flow Hedging [Member] | Embedded Aluminum Derivative [Member] | Derivatives Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amount of gain (loss) expected to be recognized into earnings over the next 12 months			(46,000,000)
Derivative instruments ineffectiveness	$ 0			0
Cash Flow Hedging [Member] | Other Comprehensive Loss [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) recognized			24,000,000	92,000,000	$ 2,000,000
Realized gain (loss) on derivatives			$ 14,000,000	$ 15,000,000
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of smelters | Smelter			9
Number of alumina refineries to be powered under supplied agreement | Refinery			3
Level 3 [Member] | Embedded Aluminum Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative			1