Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) Segment
Goodwill [Line Items]
Number of reportable segments \| Segment	5
Alumina [Member]
Goodwill [Line Items]
Segment reporting, goodwill	$ 146
Global Rolled Products [Member]
Goodwill [Line Items]
Segment reporting, goodwill	59
Engineered Products and Solutions [Member]
Goodwill [Line Items]
Segment reporting, goodwill	253
Transportation and Construction Solutions [Member]
Goodwill [Line Items]
Segment reporting, goodwill	$ 18
Alcoa [Member]
Goodwill [Line Items]
Number of reportable segments \| Segment	4

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration