Goodwill and Other Intangible Assets - Summary of Goodwill which is Included in Other Noncurret Assets (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 989	$ 989
Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	151	154
Aluminum [Member]
Goodwill [Line Items]
Goodwill	0
Accumulated impairment losses	989	989
Corporate Segment [Member]
Goodwill [Line Items]
Accumulated impairment losses	742	742
Corporate Segment [Member] | Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	146	148
Bauxite [Member]
Goodwill [Line Items]
Segment reporting, goodwill	49
Bauxite [Member] | Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	2	2
Alumina [Member]
Goodwill [Line Items]
Segment reporting, goodwill	97
Alumina [Member] | Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	$ 3	$ 4