Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Alcoa's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	35.00%	35.00%	35.00%
Taxes on foreign operations	0.40%	(3.20%)	0.70%
Permanent differences on restructuring and other charges and asset disposals	2.70%	(3.50%)	(0.80%)
Non-deductible acquisition costs	5.20%	1.70%
Equity income/loss	4.90%	3.20%	(0.70%)
Noncontrolling interests	11.40%	6.80%	(3.10%)
Statutory tax rate and law changes	(0.80%)	17.90%	0.60%
Tax holidays	(11.30%)	6.10%
Tax credits	(3.60%)	(1.30%)	0.20%
Changes in valuation allowances	135.30%	3.50%	(23.20%)
Impairment of goodwill	3.60%		(33.30%)
Company-owned life insurance/split-dollar net premiums	(2.20%)	(2.20%)	1.10%
Other	(1.20%)	0.40%	(0.10%)
Effective tax rate	179.40%	64.40%	(23.60%)