Subsequent Events	3 Months Ended
Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	R. Subsequent Events On April 1, 2021, Alcoa made $500 in discretionary contributions to certain U.S. defined benefit pension plans. The contributions were funded with net proceeds from the March 2021 debt issuance (see Note K) and available cash on hand. On April 7, 2021, Alcoa redeemed in full $750 aggregate principal amount of the 2024 Notes at a redemption price equal to 103.375% of the principal amount of the 2024 Notes, plus accrued and unpaid interest to but not including the Redemption Date.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI http://asc.fasb.org/topic&trid=2122774

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

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