Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 14, 2014
Goodwill [Line Items]
Goodwill gross, beginning balance			$ 7,006	$ 5,174
Accumulated impairment losses, beginning balance			(1,759)	(1,759)
Goodwill, beginning balance			5,247	3,415
Acquisitions			261	1,898
Divestitures			(1)	(3)
Impairment	$ (25)		(25)		$ (1,731)
Translation			(81)	(63)
Goodwill gross, ending balance	7,185	$ 5,174	7,185	7,006	5,174
Accumulated impairment losses, ending balance	(1,784)	(1,759)	(1,784)	(1,759)	(1,759)
Goodwill, ending balance	5,401	3,415	5,247	3,415	3,415
Alumina [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			8	9
Goodwill, beginning balance			8	9
Divestitures				(3)
Translation			(2)	2
Goodwill gross, ending balance	6	9	6	8	9
Goodwill, ending balance	6	9	8	9	9
Primary Metals [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			989	989
Accumulated impairment losses, beginning balance			(989)	(989)
Impairment	(25)	(1,731)
Goodwill gross, ending balance	989	989	989	989	989
Accumulated impairment losses, ending balance	(989)	(989)	(989)	(989)	(989)
Global Rolled Products [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			210	218
Goodwill, beginning balance			210	218
Divestitures			(1)
Translation			(8)	(8)
Goodwill gross, ending balance	201	218	201	210	218
Goodwill, ending balance	201	218	210	218	218
Engineered Products and Solutions [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			4,458	2,606
Goodwill, beginning balance			4,458	2,606
Acquisitions			261	1,898
Translation			(59)	(46)
Goodwill gross, ending balance	4,660	2,606	4,660	4,458	2,606
Goodwill, ending balance	4,660	2,606	4,458	2,606	2,606	$ 1,801
Transportation and Construction Solutions [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			114	117
Accumulated impairment losses, beginning balance			(28)	(28)
Goodwill, beginning balance			86	89
Impairment			(25)
Translation			(3)	(3)
Goodwill gross, ending balance	111	117	111	114	117
Accumulated impairment losses, ending balance	(53)	(28)	(53)	(28)	(28)
Goodwill, ending balance	58	89	86	89	89
Corporate [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance			1,227	1,235
Accumulated impairment losses, beginning balance			(742)	(742)
Goodwill, beginning balance			485	493
Translation			(9)	(8)
Goodwill gross, ending balance	1,218	1,235	1,218	1,227	1,235
Accumulated impairment losses, ending balance	(742)	(742)	(742)	(742)	(742)
Goodwill, ending balance	$ 476	$ 493	$ 485	$ 493	$ 493