Contingencies and Commitments - Additional Information - 1 (Detail) - USD ($) $ in Millions	1 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2009
Loss Contingencies [Line Items]
Number of cleanup locations			More than 100
Remediation reserve balance			$ 604	$ 543
Remediation reserve balance, classified as a current liability			50	70
Increase in remediation reserve	$ 1		115
Remediation reserve adjustment			86	47
Payments related to remediation expenses applied against the reserve			43	46
Increase (Decrease) in reserves due to effects of foreign currency translation			$ (16)	19
Actual remediation fieldwork period			4 years
Guarantee debt service expiration year			2019
Firth Rixson [Member]
Loss Contingencies [Line Items]
Increase (Decrease) in reserves due to acquisition			$ 5
Minimum [Member]
Loss Contingencies [Line Items]
Majority of the project funding period			2017
Maximum [Member]
Loss Contingencies [Line Items]
Majority of the project funding period			2021
Recurring Costs of Managing Hazardous Substances and Environmental Programs [Member]
Loss Contingencies [Line Items]
Percentage of cost of goods sold			2.00%
Massena West, NY [Member]
Loss Contingencies [Line Items]
Remediation reserve balance			$ 234	239
Grasse River [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve				61
Sherwin, TX site [Member]
Loss Contingencies [Line Items]
Remediation reserve balance			30	32
Expected portion of funding through 2019			15
Portovesme [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve				3		$ 3
Remediation reserve adjustment			7	3
Other Sites [Member]
Loss Contingencies [Line Items]
Remediation reserve adjustment			15	16
Massena East, Ny and Point Henry and Yennora, Australia and Portovesme [Member]
Loss Contingencies [Line Items]
Remediation reserve adjustment				42
Massena East Smelter [Member]
Loss Contingencies [Line Items]
Remediation reserve adjustment			52
East St. Louis, IL Site [Member]
Loss Contingencies [Line Items]
Remediation reserve balance			8	$ 15
Pocos De Caldas Smelter and the Anglesea Power Station [Member]
Loss Contingencies [Line Items]
Remediation reserve adjustment			29
Mosjoen [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve		$ 11	$ 12		$ 20