Other Income, Net - Additional Information (Detail) - 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, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2016
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales					$ 513	$ 156	$ 74
Pre-tax gain on sale of common stock			$ 167		167
Total amount committed under outstanding surety bonds		$ 54			54
Other, net					103	79	18
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)
Separation Agreement
Other Non operating Income Expense [Line Items]
Total amount committed under outstanding surety bonds		$ 25			25			$ 25
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
Sherwin, TX Site
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales							19
China Rolling Mill Equity Investment
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales							$ 19