Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Agreement	Mar. 31, 2012	Jan. 31, 2013
Debt Instrument [Line Items]
Line of credit facility amount outstanding			$ 150
Repayment of credit facility	150
Applicable margin on LIBOR	1.375%
Line of credit facility, expiration date	Mar. 19, 2013
Number of agreements	3
Repayment of outstanding debt	639	414
Aluminio [Member]
Debt Instrument [Line Items]
Line of credit facility amount outstanding	52
Repayment of outstanding debt	52
Weighted-average interest rate	0.72%
Weighted-average maturity days	70
First loans agreement [Member]
Debt Instrument [Line Items]
Applicable margin on LIBOR	1.25%
Third loans agreement [Member]
Debt Instrument [Line Items]
Repayment of credit facility	75
Applicable margin on LIBOR	0.95%
Term loan agreement [Member] | First loans agreement [Member]
Debt Instrument [Line Items]
Line of credit facility amount outstanding	200
Applicable margin on LIBOR	1.50%
Revolving credit agreement [Member]
Debt Instrument [Line Items]
Revolving credit facility, term	5
Revolving credit agreement [Member] | First loans agreement [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Jul. 31, 2013
Revolving credit agreement [Member] | Second loans agreement [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Feb. 28, 2014
Agreed credit facility amount	150
Revolving credit agreement [Member] | Third loans agreement [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Dec. 31, 2013
Agreed credit facility amount	$ 75