Other Expense (Income), Net - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2017	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Non operating Income Expense [Line Items]
Income tax benefit			$ (105)	$ (226)	$ (544)
Tax agreement, indemnification of ultimate liability, percent				49.00%
Net loss (gain) from asset sales			(7)	$ (10)	513
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
Firth Rixson
Other Non operating Income Expense [Line Items]
Contingent consideration arrangements, change in amount of contingent consideration, liability					81	$ 56
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