Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	AA
Entity Registrant Name	ALCOA CORP
Entity Central Index Key	0001675149
Entity File Number	1-37816
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-1789115
Entity Address, Address Line One	201 Isabella Street
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15212-5858
City Area Code	412
Local Phone Number	315-2900
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		186,724,745
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NYSE
Document Quarterly Report	true
Document Transition Report	false