Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended		3 Months Ended			9 Months Ended				3 Months Ended	9 Months Ended		9 Months Ended				9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2013	Sep. 30, 2013 D	Jun. 30, 2013 D	Mar. 31, 2013 D Agreement	Sep. 30, 2013 Agreement	Sep. 30, 2012	Dec. 31, 2012 Agreement	Jan. 31, 2012	Mar. 31, 2013 Term Loan [Member]	Sep. 30, 2013 Due on September 2014 [Member]	Sep. 30, 2013 Due on September 2015 [Member]	Sep. 30, 2013 Due on December 2013 [Member]	Sep. 30, 2013 Due on February 2014 [Member]	Sep. 30, 2013 Due on March 2014 [Member]	Sep. 30, 2013 Due on July 2014 [Member]	Mar. 31, 2013 Aluminio [Member] D	Sep. 30, 2013 6% Notes, Due 2013 [Member]	May 31, 2013 6% Notes, Due 2013 [Member]	Sep. 30, 2013 Debt Accrued and Unpaid Interest [Member]	Sep. 30, 2013 Revolving Credit Agreement [Member]	Mar. 31, 2013 Revolving Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Agreement [Member]	Sep. 30, 2013 Revolving Credit Agreement [Member] Minimum [Member]	Dec. 31, 2012 Revolving Credit Agreement [Member] Minimum [Member]	Sep. 30, 2013 Revolving Credit Agreement [Member] Maximum [Member]	Dec. 31, 2012 Revolving Credit Agreement [Member] Maximum [Member]
Debt Instrument [Line Items]
Early repayment of outstanding notes																		$ 422
Long-term debt, interest rate								6.00%										6.00%
Payments on long-term debt		325	575	625	1,980	793										52	435		12
Purchase premiums repaid recorded as interest expense					1
Number of agreements				3	9		6
Agreed credit facility amount																				1,065	425	640
Line of credit facility, expiration date										2014-09	2015-09	2013-12	2014-02	2014-03	2014-07								2013-10	2013-03	2015-12	2015-12
Agreed credit facility amount				150
Agreed credit facility amount										100	100
Repayment of outstanding debt					7	29			200
Agreed credit facility amount			150									75	150	150	200
Extension of maturity period	1 year				1 year
Revolving credit facility, term																				5 years
Weighted-average interest rate		1.58%	1.50%	1.58%												0.72%
Weighted-average days outstanding		66	72	40												70
Line of credit facility, amount outstanding		$ 325	$ 575	$ 625	$ 325											$ 52