Goodwill - Summary of Goodwill which is Included in Other Noncurrent Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Goodwill [Line Items]
Goodwill	$ 146	$ 145
Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	146	145
Alumina [Member] | Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	4	4
Corporate Segment [Member] | Other Noncurrent Assets [Member]
Goodwill [Line Items]
Goodwill	$ 142	$ 141