Debt - Schedule of Long-Term Debt (Parenthetical) (Detail)			12 Months Ended		12 Months Ended
	Aug. 31, 2012	Jan. 31, 2012	Dec. 31, 2013 6.00% Notes, Due 2013 [Member]	May 31, 2013 6.00% Notes, Due 2013 [Member]	Dec. 31, 2013 5.25% Convertible Notes, Due 2014 [Member]	Dec. 31, 2013 5.55% Notes, Due 2017 [Member]	Dec. 31, 2013 6.50% Bonds, Due 2018 [Member]	Dec. 31, 2013 6.75% Notes, Due 2018 [Member]	Dec. 31, 2013 5.72% Notes, Due 2019 [Member]	Dec. 31, 2013 6.150% Notes, Due 2020 [Member]	Dec. 31, 2013 5.40% Notes, Due 2021 [Member]	Dec. 31, 2013 5.87% Notes, Due 2022 [Member]	Dec. 31, 2013 5.90% Notes, Due 2027 [Member]	Dec. 31, 2013 6.75% Bonds, Due 2028 [Member]	Dec. 31, 2013 5.95% Notes Due 2037 [Member]	Dec. 31, 2013 BNDES Loans, Due 2014-2029 [Member]	Dec. 31, 2013 Iowa Finance Authority Loan, Due 2042 (4.75%) [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	4.75%	6.00%	6.00%	6.00%	5.25%	5.55%	6.50%	6.75%	5.72%	6.15%	5.40%	5.87%	5.90%	6.75%	5.95%		4.75%
Debt instrument, maturity date			2013		2014	2017	2018	2018	2019	2020	2021	2022	2027	2028	2037		2042
Debt instrument, maturity date start																2014
Debt instrument, maturity date end																2029