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Cash Flow Information - Additional Information (Details) $ / shares in Units, $ in Millions |  | 1 Months Ended | 3 Months Ended
--- | --- | --- | ---
Oct. 02, 2017 $ / shares shares | Sep. 30, 2014 shares | Jun. 30, 2017 USD ($) shares
Schedule Of Common Stock [Line Items] |  |  |
Depository shares sold (in shares) | 24,022 | 25,000,000 | 12,958,767
Preferred stock conversion rate |  | 0.10 |
Conversion of stock, shares converted (in shares) | 31,420 |  |
Alcoa Corporation | Electricity Contract |  |  |
Schedule Of Common Stock [Line Items] |  |  |
Outstanding notes held by Investment banks, including accrued and unpaid interest | $ |  |  | $ 465
Mandatory convertible preferred stock |  |  |
Schedule Of Common Stock [Line Items] |  |  |
Depository shares sold (in shares) | 24,975,978 |  |
Preferred stock conversion rate | 0.1 |  |
Preferred stock conversion price (in usd per share) | $ / shares | $ 1.56996 |  |
Conversion of stock, shares converted (in shares) | 39,211,286 |  |

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- Definition The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 + Details
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