Derivatives and Other Financial Instruments - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended		12 Months Ended						12 Months Ended				1 Months Ended
	Jul. 31, 2012 Contract Plant	Jan. 31, 2012	Dec. 31, 2013 USD ($) Contract t	Dec. 31, 2013 CAD Contract t	Dec. 31, 2011 USD ($)	Dec. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Aug. 31, 2012	Dec. 31, 2013 Forward Contracts [Member] USD ($)	Dec. 31, 2013 Forward Contracts [Member] BRL	Dec. 31, 2013 Level 3 [Member] USD ($)	Dec. 31, 2012 Level 3 [Member] USD ($)	Jul. 31, 2012 Power Contracts One [Member]	Jul. 31, 2012 Power Contracts Two [Member]	Jan. 31, 2012 Interest Rate Swap [Member] USD ($)	Dec. 31, 2011 Interest Rate Swap [Member] USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized loss on derivative contracts											$ 76	$ 88
Other derivative contracts estimated term of quoted market prices, in years			10 years	10 years
Number of contracts	2
Power contracts maturity date													Mar. 31, 2014	Mar. 31, 2016
Number of smelters	2
Derivative asset amount			390			596	596				355	550
Power purchase period forecasted by derivative instrument			Through December 2036	Through December 2036
Period of natural gas supply contract			6 years	6 years
Number of commodities involved for valuation of supply contract			2	2
Number of contracts ceased to qualify as fair value hedge			0	0
Amount of aluminum kmt designated as fair value hedges			412,000	412,000
Derivative designated as fair value hedge start period			2014	2014
Derivative designated as fair value hedge end period			2017	2017
Face amount of debt the hedges effectively convert from fixed to floating through 2018			200
Notional amount of interest rate swaps															315	550
Long-term debt, interest rate		6.00%						4.75%
Long-term debt, maturity date		2012
Gain on termination of interest rate swaps					33
Interest rate cash flow hedges			0		0	0
Forward contract to purchase to mitigate the foreign currency risk related to a Canadian/Brazilian-denominated loan due in 2014			$ 54	58					$ 231	543
Maturity date of forward contract									Mar. 31, 2014	Mar. 31, 2014