Restructuring and Other Charges (2015 Actions) - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) kt	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) kt Employees kT
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 297,000,000	$ 209,000,000	$ 309,000,000	$ 318,000,000	$ 983,000,000
Amount related to legal matters			$ (22,000,000)		201,000,000
Capacity closure | kt			191
Asset impairment charges			$ 40,000,000	155,000,000	311,000,000
2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					983,000,000
Amount related to legal matters					$ 201,000,000
Capacity of lines under review period					12 months
Capacity of lines under review | kt					2,800
Capacity of smelting lines under review | kt					500
Inventory write down					$ 90,000,000
Amount of cash payments expected to be paid beyond the end of the current annual period			4,000,000
2015 Restructuring Plans Action [Member] | Pension Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 30,000,000
2015 Restructuring Plans Action [Member] | Suriname [Member]
Restructuring Cost and Reserve [Line Items]
Capacity closure | kT					1,330,000
2015 Restructuring Plans Action [Member] | Sao Luis Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Capacity closure | kT					74,000
2015 Restructuring Plans Action [Member] | TEXAS
Restructuring Cost and Reserve [Line Items]
Curtailment capacity | kT					2,010,000
Remaining curtailment capacity | kT					1,635,000
2015 Restructuring Plans Action [Member] | WASHINGTON
Restructuring Cost and Reserve [Line Items]
Curtailment capacity | kT					143,000
2015 Restructuring Plans Action [Member] | Warrick, IN Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Capacity closure | kT					269,000
2015 Restructuring Plans Action [Member] | Pocos de Caldas Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Capacity closure | kT					96
2015 Restructuring Plans Action [Member] | Point Henry Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Percentage of power supply					40.00%
Exit Cost [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 418,000,000
Shutdown Costs [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					238,000,000
Divested Businesses [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					24,000,000
Restructuring Programs Layoffs 2014 [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 45,000,000
Number of employees associated with layoff costs | Employees					465
Asset Impairment [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 33,000,000
Miscellaneous Charges [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					1,000,000
Other Adjustments [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					7,000,000
Corporate Restructuring Charges [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					32,000,000
Shutdown and Curtailment Actions [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Asset impairment charges					$ 226,000,000
Number of employees associated with layoff costs | Employees					3,100
Shutdown and Curtailment Actions [Member] | 2015 Restructuring Plans Action [Member] | Primary Metals [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | Employees					1,800
Shutdown and Curtailment Actions [Member] | 2015 Restructuring Plans Action [Member] | Alumina [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | Employees					1,300
Layoff Costs [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 154,000,000
Asset Impairment and Accelerated Depreciation [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					85,000,000
Other Exit Costs [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					222,000,000
Asset Retirement Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			10,000,000	97,000,000	76,000,000
Asset Retirement Obligations [Member] | 2015 Restructuring Plans Action [Member] | Historical [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					72,000,000
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			8,000,000	26,000,000	86,000,000
Environmental Remediation [Member] | 2015 Restructuring Plans Action [Member] | Historical [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					85,000,000
Supplier and Customer Contract [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					65,000,000
Restructuring Programs Layoffs 2015 [Member] | 2015 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments made against the layoff reserves			$ 18,000,000	$ 65,000,000	$ 26,000,000