Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Millions		10 Months Ended	12 Months Ended
	Nov. 01, 2016 USD ($) $ / shares shares	Oct. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) Country Location $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)
Basis Of Presentation [Line Items]
Number of countries in which entity operates | Country			10
Separation based on pro rata distribution percentage on common stock	80.10%
Common stock conversion ratio	0.333
Cash payment related to separation transaction	$ 1,072			$ 247	$ 1,072
Proceeds from sale of assets				$ 243
Common stock distributed related to separation transaction | shares	146,159,428
Common stock sold | shares				36,311,767
Common stock par value | $ / shares	$ 0.01		$ 0.01	$ 0.01
Costs related to separation transaction		$ 152
Proceeds from noncontrolling shareholder			$ 149	$ 80	48
Aluminum Segment [Member]
Basis Of Presentation [Line Items]
Ownership interest in joint venture			55.00%
Alumina Limited [Member]
Basis Of Presentation [Line Items]
Proceeds from noncontrolling shareholder			$ 149	$ 80	$ 48
AWAC [Member] | Alumina Limited [Member]
Basis Of Presentation [Line Items]
Non-controlling interest, ownership percentage			40.00%
Alcoa Corporation [Member]
Basis Of Presentation [Line Items]
Minority interest percentage	25.10%		25.10%
Costs related to separation transaction		$ 68
Alcoa Corporation [Member] | AWAC [Member]
Basis Of Presentation [Line Items]
Ownership interest percentage			60.00%
Parent Co [Member]
Basis Of Presentation [Line Items]
Percentage of common stock retained	19.90%
Common stock shares retained | shares	36,311,767
Minimum [Member]
Basis Of Presentation [Line Items]
Number of operating locations | Location			40
Maximum [Member]
Basis Of Presentation [Line Items]
Percent of equity investments in other entity			50.00%