Acquisitions and Divestitures - 2014 Acquisitions - Additional Information (Detail)				1 Months Ended		3 Months Ended	12 Months Ended
	Nov. 19, 2014 USD ($) $ / shares	Jun. 16, 2014 $ / shares shares	Jun. 15, 2014 $ / shares shares	Aug. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) Facilities Employees	Nov. 18, 2014 $ / shares
Business Acquisition [Line Items]
Interest expenses							$ 499,000,000	$ 473,000,000	$ 442,000,000
Goodwill						$ 5,148,000,000	5,148,000,000	5,249,000,000	5,087,000,000
Income tax expense							$ 1,476,000,000	$ 339,000,000	$ 174,000,000
Weighted average amortization period of intangible asset							35 years
Alcoa Fastening Systems and Rings [Member]
Business Acquisition [Line Items]
Goodwill						1,117,000,000	$ 1,117,000,000
Alcoa Forging and Extrusions [Member]
Business Acquisition [Line Items]
Goodwill						684,000,000	684,000,000
Firth Rixson [Member]
Business Acquisition [Line Items]
Business acquisition purchase price	$ 2,995,000,000				$ 2,850,000,000
Cash paid for business acquisition	2,385,000,000				2,350,000,000
Value of common stock issued	$ 610,000,000				$ 500,000,000
Common stock issued as part of acquisition | shares		36,523,010	12,174,337
Business acquisition agreement date					Dec. 31, 2020
Business acquisition common stock issued, price per share | $ / shares	$ 50.07	$ 13.69	$ 41.07							$ 16.69
Business acquisition transaction cost	$ 35,000,000
Professional fees and costs					$ 42,000,000
Professional fees and costs, after tax					34,000,000
Interest expenses					13,000,000
Interest expenses, after tax					8,000,000
Business acquisition, unsecured bridge term loan					2,500,000,000
Number of operating facilities | Facilities									13
Number of employees | Employees									2,400
Business acquisition sales									$ 81,000,000
After-tax operating income									$ (12,000,000)
Goodwill						1,801,000,000	1,801,000,000
Income tax expense							0
Business acquisition potential earn-out						150,000,000	$ 150,000,000
Business combination contingent consideration earnout period description							2019 through 2020
Fair value liability reduced						$ 56,000,000
Firth Rixson [Member] | Maximum [Member]
Business Acquisition [Line Items]
Business acquisition potential earn-out					$ 150,000,000
Aluminum Brazing Sheet [Member]
Business Acquisition [Line Items]
Percentage of outstanding non controlling interest				30.00%
Amount of outstanding non controlling interest				$ 28,000,000