Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 EUR (€)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Assessment for 2006 through 2009 tax years	$ 152	€ 129
Guarantees of third party related to project financing	25
Letters of credit, total amount committed	$ 127
Letters of credit, expiration date	2017
Total amount committed under outstanding surety bonds	$ 128
Surety bonds, expiration date	2017
Other Noncurrent Liabilities and Deferred Credits [Member]
Loss Contingencies [Line Items]
Combined fair value of guarantees	$ 35			$ 35
Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	270			354
Total amount committed under outstanding surety bonds	25
Supply Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	1,660
Purchase Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing				$ 245
Alcoa Corporation Energy Supply Contracts Guarantee [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 50
Alcoa Corporation Environmental Liabilities Guarantee [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	53
Alcoa Corporation Workers Compensation Claims [Member]
Loss Contingencies [Line Items]
Letters of credit, total amount committed	61
Alcoa Corporation Equipment Leases And Energy Contracts [Member]
Loss Contingencies [Line Items]
Letters of credit, total amount committed	$ 103
Minimum [Member] | Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2017
Minimum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2017
Maximum [Member] | Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2024
Maximum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2026