Debt - Schedule of Long-Term Debt (Parenthetical) (Detail)			12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Jan. 31, 2012	Dec. 31, 2012 6% Notes, due 2012 [Member]	Jan. 31, 2012 6% Notes, due 2012 [Member]	Dec. 31, 2012 6% Notes, due 2013 [Member]	Dec. 31, 2011 6% Notes, due 2013 [Member]	Dec. 31, 2012 5.25% Convertible Notes, due 2014 [Member]	Dec. 31, 2012 5.55% Notes, due 2017 [Member]	Dec. 31, 2012 6.5% Bonds, due 2018 [Member]	Dec. 31, 2012 6.75% Notes, due 2018 [Member]	Dec. 31, 2012 5.72% Notes, due 2019 [Member]	Dec. 31, 2012 6.15% Notes, due 2020 [Member]	Dec. 31, 2012 5.40% Notes, due 2021 [Member]	Dec. 31, 2012 5.87% Notes, due 2022 [Member]	Dec. 31, 2012 5.9% Notes, due 2027 [Member]	Dec. 31, 2012 6.75% Bonds, due 2028 [Member]	Dec. 31, 2012 5.95% Notes due 2037 [Member]	Dec. 31, 2012 BNDES Loans, due 2013-2029 [Member]	Dec. 31, 2012 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%	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			2012		2013		2014	2017	2018	2018	2019	2020	2021	2022	2027	2028	2037		2042
Debt instrument, maturity date range, start																		2013