Other Expense (Income), Net - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Non operating Income Expense [Line Items]
Income tax benefit					$ (226)	$ (544)	$ (1,476)
Tax agreement, indemnification of ultimate liability, percent					49.00%
Net loss (gain) from asset sales					$ (10)	513	(11)
Pre-tax gain on sale of common stock			$ 167		167
Total amount committed under outstanding surety bonds					50
Separation Agreement
Other Non operating Income Expense [Line Items]
Total amount committed under outstanding surety bonds		$ 25				25
Firth Rixson
Other Non operating Income Expense [Line Items]
Contingent consideration arrangements, change in amount of contingent consideration, liability		$ (81)		$ (56)		$ 81	56
Business combination, post acquisition closing adjustment							$ (20)
Alcoa Corporation
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales					351
Pre-tax gain on sale of common stock	$ 351
Spain | Other Nonoperating Income (Expense) | Alcoa Corporation
Other Non operating Income Expense [Line Items]
Income tax benefit					$ 29