Restructuring and Other Charges - 2016 Actions (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) employee position	Dec. 31, 2016 USD ($)	Dec. 31, 2016 facility	Dec. 31, 2016 employee	Dec. 31, 2016 position	Dec. 31, 2015 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 165	$ 155				$ 214
Restructuring and other charges after tax	$ 143	114				192
Number of employees associated with layoff costs | position	880
Layoff costs	$ 64	70				97
United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee				60
Other exit costs		4
Layoff costs		2
Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		21
Number of employees associated with layoff costs | position					145
Other exit costs		9
Layoff costs		7
RTI
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		3
Restructuring and other charges after tax		2
Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	400
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	245
Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	135
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 11	23				39
Number of employees associated with layoff costs | position	100
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 69	57
Restructuring and other charges after tax	$ 47	46
Other exit costs | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		2
Shutdown and Curtailment Actions
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		37
Restructuring and other charges after tax		24
Closure Of Five Facility
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		20
Restructuring and other charges after tax		14
Number of facilities closed | facility			5
Number of employees associated with layoff costs | position					280
Restructuring Programs Layoffs 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		53
Restructuring and other charges after tax		33
Number of employees associated with layoff costs	1,700			1,750	1,315
Approximate number of employees already laid off | employee	1,280
Restructuring charges for layoffs	$ 26	16
Restructuring Programs Layoffs 2016 | Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					1,045
Restructuring Programs Layoffs 2016 | Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					30
Restructuring Programs Layoffs 2016 | Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					30
Restructuring Programs Layoffs 2016 | Corporate
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					210
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	12	11				7
Restructuring and other charges after tax		8				4
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2
Restructuring and other charges after tax		1
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (11)	25				8
Restructuring and other charges after tax		12				$ 3
Asset Impairment and Accelerated Depreciation | United Kingdom
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		51
Asset Retirement Obligations | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		4
Environmental Remediation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2
Environmental Remediation | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		$ 3