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Debt - Additional Information (Detail) - USD ($) |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 07, 2021 | Apr. 01, 2021 | Mar. 04, 2021 | Mar. 03, 2021 | Mar. 31, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2021
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
U.S. defined benefit pension plans, company's contribution |  | $ 500,000,000 |  |  |  |  |  |
Premium paid on early redemption of debt |  |  |  |  |  |  |  | $ 25,000,000
5.500% Senior Notes due 2027 [Member] | Alcoa Nederland Holding BV [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt redemption description |  |  |  |  |  |  |  | ANHBV has the option to redeem the 2029 Notes on at least 10 days, but not more than 60 days, prior notice to the holders of the 2029 Notes under multiple scenarios, including, in whole or in part, at any time or from time to time after March 31, 2024, at a redemption price specified in the indenture (up to 102.063% of the principal amount plus any accrued and unpaid interest in each case). Also, the 2029 Notes are subject to repurchase upon the occurrence of a change in control repurchase event (as defined in the indenture) at a repurchase price in cash equal to 101% of the aggregate principal amount of the 2029 Notes repurchased, plus any accrued and unpaid interest on the 2029 Notes repurchased.
4.125% Senior Notes due 2029 [Member] | Alcoa Nederland Holding BV [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Senior notes, interest percentage |  |  |  |  | 4.125% |  | 4.125% |
Debt instrument maturity date |  |  |  |  | 2029 |  |  |
Principal amount of debt |  |  |  |  | $ 500,000,000 |  | $ 500,000,000 |
Proceeds from issuance of debt |  |  |  |  | $ 493,000,000 |  |  |
U.S. defined benefit pension plans, company's contribution |  | 500,000,000 |  |  |  |  |  |
Debt instrument, frequency of periodic payment |  |  |  |  |  |  |  | semi-annually
Debt instrument, date of first required payment |  |  |  |  | Sep. 30, 2021 |  |  |
6.75% Notes, due 2024 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument maturity date | 2024 |  |  |  |  |  |  |
Redemption of senior note | $ 750,000,000 |  |  |  |  |  |  |
Premium paid on early redemption of debt |  |  |  |  |  | $ 32,000,000 |  |
6.75% Notes, due 2024 [Member] | Alcoa Nederland Holding BV [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Senior notes, interest percentage |  |  |  |  | 6.75% |  | 6.75% |
Debt instrument maturity date |  |  |  |  | 2024 |  |  |
Principal amount of debt |  |  |  |  | $ 750,000,000 |  | $ 750,000,000 |
Maximum [Member] | 5.500% Senior Notes due 2027 [Member] | Alcoa Nederland Holding BV [Member] | After June 15, 2023 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument redemption period |  |  |  |  |  |  |  | 60 days
Debt instrument redemption price percentage |  |  |  |  |  |  |  | 102.063%
Maximum [Member] | 5.500% Senior Notes due 2027 [Member] | Alcoa Nederland Holding BV [Member] | Change in Control [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument redemption price percentage |  |  |  |  |  |  |  | 101.00%
Maximum [Member] | 6.75% Notes, due 2024 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument redemption price percentage | 103.375% |  |  |  |  |  |  |
Minimum [Member] | 5.500% Senior Notes due 2027 [Member] | Alcoa Nederland Holding BV [Member] | After June 15, 2023 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument redemption period |  |  |  |  |  |  |  | 10 days
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, maximum additional borrowings |  |  | $ 750,000,000 |  |  | 3,034,000,000 |  | $ 3,034,000,000
Line of credit facility, outstanding borrowings |  |  | $ 1,500,000,000 |  |  | 0 |  | 0
Amounts borrowed under the credit facility |  |  |  |  |  | $ 0 |  | $ 0
Revolving Credit Facility [Member] | 5.500% Senior Notes due 2027 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, decrease in aggregate amount of commitments |  |  |  |  |  |  | 245,000,000 |
Line of credit facility, aggregate amount of commitments |  | $ 1,500,000,000 |  |  |  |  | $ 1,255,000,000 |
Senior notes, interest percentage |  |  |  |  | 5.50% |  | 5.50% |
Debt instrument maturity date |  |  |  |  |  |  | 2027 |
Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Leverage ratio |  |  | 275.00% | 250.00% |  |  |  |
Leverage ratio, maximum possible increase |  |  | 300.00% |  |  |  |  |
Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest expense coverage ratio required to be maintained |  |  | 4.00 | 5.00 |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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