Restructuring and Other Charges, Net - Schedule of Restructuring and Other Charges by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 113	$ (19)
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	109	4
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	4	(23)
Bauxite [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	1
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	1	(1)
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 107	$ 5