Restructuring and Other Charges - Schedule of Restructuring and Other Charges by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 297	$ 209	$ 309	$ 318	$ 983
Restructuring and other charges	$ 297	$ 209	309	318	983
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			56	142	210
Restructuring and other charges			56	142	210
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			253	176	773
Restructuring and other charges			253	176	773
Bauxite [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			2	(5)	8
Restructuring and other charges			2	(5)	8
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			3	72	102
Restructuring and other charges			3	72	102
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			51	75	100
Restructuring and other charges			$ 51	$ 75	$ 100