Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions		3 Months Ended	12 Months Ended
	Oct. 05, 2016 shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2016 USD ($) Reporting_Unit shares	Dec. 31, 2015 USD ($) shares	Oct. 04, 2016 shares	Jul. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares	Nov. 14, 2014 USD ($)	Dec. 31, 2013 shares
Summary Of Significant Accounting Policies [Line Items]
Reverse stock split ratio	0.33		0.33
Common stock share outstanding | shares	400,000,000	1,310,160,141	438,519,780	1,310,160,141	1,300,000,000			1,216,663,661		1,071,011,162
Original maturity of cash equivalents			3 months
Segment Allocation, Goodwill Recognized		$ 5,249	$ 5,148	$ 5,249				$ 5,087
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			3
Goodwill impairment				25
Businesses expected to be disposed within, years			1 year
Change due to recent accounting guidance			$ 51
TITAL [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized							$ 118
RTI [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized			$ 298
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	$ 4,579	4,660				4,458	$ 1,801
Number of reporting units for goodwill allocation | Reporting_Unit			2
Engineered Products and Solutions [Member] | TITAL [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized							$ 117
Transportation and Construction Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units being subjected to goodwill impairment test | Reporting_Unit			8
Number of reporting units | Reporting_Unit			3
Segment Allocation, Goodwill Recognized		58	$ 57	58				86
Goodwill impairment				25
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						$ 298
Global Rolled Products [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized		201	$ 181	$ 201				$ 210
Qualitative assessment for reporting units | Reporting_Unit			4
Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Implied fair value of goodwill			$ 0
Goodwill impairment		$ 25
Alcoa Fastening Systems and Rings [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized			1,117
Alcoa Fastening Systems and Rings [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized			2,200
Alcoa Power and Propulsion [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Segment Allocation, Goodwill Recognized			$ 1,647
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units being subjected to goodwill impairment test | Reporting_Unit			4
Minimum [Member] | Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of total goodwill allocated to reporting units			70.00%