Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) Reporting_Unit	Dec. 31, 2013 USD ($)	Jan. 01, 2016 USD ($)	Jul. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Nov. 14, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity								40.00%
Original maturity of cash equivalents			3 months
Segment Allocation, Goodwill Recognized	$ 5,401,000,000	$ 3,415,000,000	$ 5,401,000,000	$ 3,415,000,000				$ 5,247,000,000
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill			50.00%
Qualitative assessment for reporting units | Reporting_Unit			7
Goodwill impairment	25,000,000		$ 25,000,000	1,731,000,000
Maximum hedging contracts period, in years			5 years
Businesses expected to be disposed within, years			1 year
Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Change due to recent accounting guidance					$ 58,000,000
TITAL [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized							$ 118,000,000
RTI [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized	240,000,000		$ 240,000,000
Deferred Income Tax Non Current [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets and liabilities prior period reclassification adjustment			421,000,000
Other Noncurrent Liabilities and Deferred Credits [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets and liabilities prior period reclassification adjustment			83,000,000
Non Current Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets and liabilities prior period reclassification adjustment			(385,000,000)
Noncurrent Liability [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets and liabilities prior period reclassification adjustment			$ (47,000,000)
Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | Reporting_Unit			4
Segment Allocation, Goodwill Recognized	4,660,000,000	2,606,000,000	$ 4,660,000,000	2,606,000,000				4,458,000,000	$ 1,801,000,000
Number of reporting units for goodwill allocation | Reporting_Unit			2
Qualitative assessment for reporting units | Reporting_Unit			4
Engineered Products and Solutions [Member] | TITAL [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized							$ 118,000,000
Transportation and Construction Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units being subjected to goodwill impairment test | Reporting_Unit			10
Number of reporting units | Reporting_Unit			3
Segment Allocation, Goodwill Recognized	58,000,000	89,000,000	$ 58,000,000	89,000,000				86,000,000
Qualitative assessment for reporting units | Reporting_Unit			2
Goodwill impairment			$ 25,000,000
Other Operating Segments [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | Reporting_Unit			3
Titanium Engineered Products [Member] | RTI [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized						$ 240,000,000
Global Rolled Products [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized	201,000,000	218,000,000	$ 201,000,000	218,000,000				$ 210,000,000
Qualitative assessment for reporting units | Reporting_Unit			2
Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Implied fair value of goodwill			$ 0	$ 0
Goodwill impairment	25,000,000	1,731,000,000
Goodwill impairment after noncontrolling interest		$ 1,719,000,000
Alcoa Fastening Systems and Rings [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized	1,117,000,000		1,117,000,000
Alcoa Fastening Systems and Rings [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized	2,232,000,000		2,232,000,000
Alcoa Power and Propulsion [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized	$ 1,695,000,000		$ 1,695,000,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units being subjected to goodwill impairment test | Reporting_Unit			2
Minimum [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of total goodwill allocated to reporting units			70.00%
Minimum [Member] | Bauxite Mining [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of mining			1 year
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity	50.00%		50.00%
Number of reporting units being subjected to goodwill impairment test | Reporting_Unit			3
Maximum [Member] | Bauxite Mining [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of mining			5 years