| Document And Entity Information | Sep. 20, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | Alcoa Corp |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Central Index Key | 0001675149 |
| Document Period End Date | Sep. 20, 2019 |
| Entity Emerging Growth Company | false |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of each class | Common Stock, par value $0.01 per share |
| Trading Symbol | AA |
| Name of each exchange on which registered | NYSE |
