Preferred and Common Stock - Additional Information (Detail) - USD ($)		1 Months Ended	2 Months Ended	12 Months Ended
	Nov. 01, 2016	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2018
Class of Stock [Line Items]
Preferred stock, authorized (in shares)		100,000,000		100,000,000
Preferred stock, par value (in dollars per share)		$ 0.01		$ 0.01
Preferred stock, issued (in shares)		0		0	0
Common stock shares authorized		750,000,000		750,000,000
Common stock par value	$ 0.01	$ 0.01		$ 0.01	$ 0.01
Common stock shares issued	182,471,195	184,770,249		184,770,249	185,200,713
Common stock distributed related to separation transaction	146,159,428
Common stock shares retained by ParentCo	36,311,767
Common stock shares outstanding		184,770,249		184,770,249	185,200,713
Common stock were reserved for future issuance		25,977,146		25,977,146
Common stock repurchase program, authorized amount							$ 200,000,000
Common stock dividends declared during period			$ 0	$ 0	$ 0
Increase in exercise price	$ 1.34
Adjusted exercise option price	$ 28.72	$ 21.44		$ 21.44
Number of options, Outstanding		1,959,927		1,959,927
Stock based compensation expense				$ 35,000,000	24,000,000	$ 28,000,000
Expense related to the acceleration of expense related to retirement-eligible employees				5,000,000	4,000,000	7,000,000
Stock-based compensation expense capitalized				$ 0	$ 0	$ 0
Fair value of stock options granted				$ 21.32	$ 12.45	$ 2.12
Volatility				43.32%
Average risk-free interest rate				2.63%
Dividend yield				0.00%
Annual pre- and post-vesting forfeitures				4.00%
Exercise behavior				63.00%
Life (years)				6 years
Description of reverse stock split				ParentCo’s stock-based compensation plan to Alcoa Corporation employees) were adjusted to reflect both the impact of ParentCo’s 1-for-3 reverse stock split that occurred on October 5, 2016 and to maintain the intrinsic value of the stock options as a result of the Separation Transaction.
Number of options, Outstanding weighted average remaining contractual life				5 years 6 months
Total intrinsic value of options outstanding		$ 8,000,000		$ 8,000,000
Stock options vested				1,298,021
Stock option exercisable				1,298,021
Weighted average exercise price, vested and exercisable		$ 26.18		$ 26.18
Cash received from option exercises				$ 23,000,000	$ 43,000,000	$ 10,000,000
Total intrinsic value of options exercised				$ 26,000,000	$ 24,000,000	$ 4,000,000
Number of options, Vested and expected to vestweighted average remaining contractual life				4 years 4 months 6 days
Total intrinsic value of options vested and exercisable		$ 5,000,000		$ 5,000,000
Unrecognized compensation costs on non-vested stock option grants (pretax)		$ 32,000,000		$ 32,000,000
Unrecognized compensation costs on non-vested awards, weighted average period of recognition in years				1 year 7 months 24 days
Alcoa Corporation [Member]
Class of Stock [Line Items]
Fair value of stock options granted						$ 4.75
Employees [Member]
Class of Stock [Line Items]
Stock based compensation expense						$ 16,000,000
Minimum [Member]
Class of Stock [Line Items]
Stock based compensation expense, stock units percentage				80.00%	80.00%	80.00%
Maximum [Member]
Class of Stock [Line Items]
Stock based compensation expense, stock units percentage				90.00%	90.00%	90.00%
Stock Units [Member]
Class of Stock [Line Items]
Number of units, Outstanding	2,605,423	2,305,145		2,305,145	2,301,332
Stock granted, Fair value				$ 52.81
Stock Units [Member] | Cliff Vest [Member]
Class of Stock [Line Items]
Vesting rights percentage				0.3333%
Restricted Stock [Member]
Class of Stock [Line Items]
Volatility				38.47%
Average risk-free interest rate				2.17%
Stock granted, Fair value				$ 73.13	$ 52.01
Restricted Stock [Member] | Standard & Poor's 500 [Member]
Class of Stock [Line Items]
Volatility				12.12%
Common Stock [Member]
Class of Stock [Line Items]
Shares issued for employee stock-based compensation plans			459,800	1,293,336	2,269,718
Repurchase of common stock shares		1,723,800
Repurchase of common stock value		$ 50,000,000
Stock Options [Member]
Class of Stock [Line Items]
Adjusted exercise option price		$ 28.41		$ 28.41	$ 25.48
Number of options, Outstanding	4,673,829	1,959,927		1,959,927	2,687,107
Stock option exercisable				896,645
Stock Options [Member] | Grade Vest [Member]
Class of Stock [Line Items]
Vesting rights percentage				0.3333%
Commom stock service period				3 years
Common stock contractual term				10 years