Preferred and Common Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 31, 2011	Jan. 31, 2010	Dec. 31, 2012	Dec. 31, 2012 Y	Dec. 31, 2011 Y	Dec. 31, 2010
Class of Stock [Line Items]
Common Stock authorized			1,800,000,000	1,800,000,000
Common stock, par value per share			$ 1	$ 1
Common stock issued, in shares			1,177,906,557	1,177,906,557	1,177,906,557
Common stock, dividends yield			$ 0.03	$ 0.12	$ 0.12	$ 0.12
Newly issued common stock, shares	36,518,563	44,313,146
Newly issued common stock, par value	$ 16.43	$ 13.54
Newly issued common stock, aggregate value	$ 600	$ 600
Percentage of funded status of pension plans	80.00%
Number of shares reserved for issuance upon conversion of convertible notes, shares				110,000,000
Number of shares reserved for issuance under Alcoa's stock-based compensation plans, shares				86,000,000
Number of years of sales and profitability targets to ascertain grant of performance stock awards				3	3
Expense related to the acceleration of expense related to retirement-eligible employees				13	18	19
Average period of dividend yield				One-year
Total intrinsic value of options exercised				2	34	8
Cash received from option exercises				12	37	13
Total tax benefit realized from these exercises				1	11	2
Unrecognized compensation costs on non-vested stock option grants (pretax)			22	22
Unrecognized compensation costs on non-vested stock option awards (pretax)			$ 35	$ 35
Unrecognized compensation costs on non-vested awards, weighted average period of recognition in years				1 year 6 months
Preferred Class A [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized			660,000	660,000
Preferred stock, par value per share			$ 100	$ 100
Cumulative dividend preference per share				$ 3.75
Preferred stock, shares outstanding			546,024	546,024	546,024
Preferred Class B [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized			10,000,000	10,000,000
Preferred stock, par value per share			$ 1	$ 1
Stock Awards [Member]
Class of Stock [Line Items]
Vesting period				three