Restructuring and Other Charges - 2016 Actions (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) position	Dec. 31, 2016 USD ($) facility position employee
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 9	$ 165	$ 155
Restructuring and other charges after tax		9	$ 143	114
Number of employees associated with layoff costs | position			880
Layoff costs		20	$ 64	68
Cash payments for restructuring		49	$ 65	$ 86
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
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		19	$ 69	57
Restructuring and other charges after tax		15	47	46
Cash payments for restructuring		2	6	13
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 | position				1,315
Cash payments for restructuring		4
Restructuring charges for layoffs			28
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
Restructuring and other charges after tax				8
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 96	96		2
Restructuring and other charges after tax		75		1
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		8	(11)	25
Restructuring and other charges after tax				12
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 | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs				3
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		20
Restructuring and other charges after tax		$ 17
Restructuring charges for layoffs			$ 26	$ 16