Separation Transactions - Additional Information (Details)				1 Months Ended			2 Months Ended	3 Months Ended		12 Months Ended
	Feb. 08, 2019 company	Oct. 02, 2017 shares	May 04, 2017	Feb. 28, 2017 USD ($) $ / shares shares	Nov. 30, 2016 shares	Sep. 30, 2014 shares	May 31, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Jun. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 07, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of independent, publicly-traded companies resulting from proposed separation transaction | company	2
Restructuring and other charges										$ 620,000,000	$ 9,000,000	$ 165,000,000
Common stock sold (in shares) | shares		24,022				25,000,000			12,958,767
Common stock sold per share (usd per share) | $ / shares									$ 35.91
Pre-tax gain on sale of common stock									$ 167,000,000			167,000,000
Proceeds from Alcoa Corporation's sale of Yadkin Hydroelectric Project										(2,000,000)	$ (1,000,000)	243,000,000
Costs related to separation transaction, pre-tax								$ 34,000,000
Costs related to separation transaction, after-tax								$ 28,000,000
Selling, General Administrative, and Other Expenses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs related to separation transaction, pre-tax												18,000,000
Costs related to separation transaction, after-tax												12,000,000
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of common stock retained					19.90%
Number of common stock retained (in shares) | shares					36,311,767
Common stock sold (in shares) | shares				23,353,000			12,958,767
Common stock sold per share (usd per share) | $ / shares				$ 38.03
Cash proceeds sale of common stock				$ 888,000,000
Pre-tax gain on sale of common stock				$ 351,000,000
Proceeds from Alcoa Corporation's sale of Yadkin Hydroelectric Project												$ 243,000,000
Percentage of ownership after transaction			0.00%
Investment Banks
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, face amount									$ 805,000,000
Common stock sold per share (usd per share) | $ / shares							$ 35.91
Pre-tax gain on sale of common stock							$ 167,000,000
Other Restructuring | Proposed Separation Transaction | Selling, General Administrative, and Other Expenses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring and other charges										$ 78,000,000
Subsequent Event | Second-Lien Notes Due 2028
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, face amount													$ 600,000,000
Convertible notes, interest rate percentage													6.125%