Contingencies and Commitments - Summary of Activity Related to Alba Matter (Detail) € in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Commitments Contingencies And Litigation [Line Items]
Government investigations	$ 735	€ 150	$ 1,195	$ 1,168	$ 782
Income (loss) before income taxes			248	497	(1,816)
Benefit for income taxes			445	320	428
Net (loss) income			$ (197)	$ 177	(2,244)
Alba [Member]
Commitments Contingencies And Litigation [Line Items]
Income (loss) before income taxes					384	$ 85
Benefit for income taxes					66	18
Net (loss) income					318	67
Alba [Member] | Government Investigation [Member]
Commitments Contingencies And Litigation [Line Items]
Government investigations					384
Alba [Member] | Civil Suit [Member]
Commitments Contingencies And Litigation [Line Items]
Civil suit						85
Alcoa [Member] | Alba [Member]
Commitments Contingencies And Litigation [Line Items]
Reallocation of civil suit					21
Reallocation of legal costs					20
Income (loss) before income taxes					367	51
Benefit for income taxes					66	18
Net (loss) income					301	33
Alcoa [Member] | Alba [Member] | Government Investigation [Member]
Commitments Contingencies And Litigation [Line Items]
Government investigations					326
Alcoa [Member] | Alba [Member] | Civil Suit [Member]
Commitments Contingencies And Litigation [Line Items]
Civil suit						51
Alumina [Member] | Alba [Member]
Commitments Contingencies And Litigation [Line Items]
Reallocation of civil suit					(21)
Reallocation of legal costs					(20)
Income (loss) before income taxes					17	34
Net (loss) income					17	34
Alumina [Member] | Alba [Member] | Government Investigation [Member]
Commitments Contingencies And Litigation [Line Items]
Government investigations					$ 58
Alumina [Member] | Alba [Member] | Civil Suit [Member]
Commitments Contingencies And Litigation [Line Items]
Civil suit						$ 34