Debt - Schedule of Long-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 8,776	$ 9,085
Less: amount due within one year	465	445
Long-term debt, excluding amount due within one year	8,311	8,640
6% Notes, due 2012 [Member]
Debt Instrument [Line Items]
Long-term debt		322
6% Notes, due 2013 [Member]
Debt Instrument [Line Items]
Long-term debt	422	422
5.25% Convertible Notes, due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt	575	575
5.55% Notes, due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	750	750
6.5% Bonds, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	250	250
6.75% Notes, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	750	750
5.72% Notes, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	750	750
6.15% Notes, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	1,000	1,000
5.40% Notes, due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt	1,250	1,250
5.87% Notes, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	627	627
5.9% Notes, due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	625	625
6.75% Bonds, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt	300	300
5.95% Notes due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt	625	625
BNDES Loans, due 2013-2029 [Member]
Debt Instrument [Line Items]
Long-term debt	397	627
Iowa Finance Authority Loan, due 2042 (4.75%) [Member]
Debt Instrument [Line Items]
Long-term debt	250
Other [Member]
Debt Instrument [Line Items]
Long-term debt	$ 205	$ 212