Debt - Schedule of Long-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 8,262	$ 8,776
Less: amount due within one year	655	465
Long-term debt, excluding amount due within one year	7,607	8,311
6.00% Notes, Due 2013 [Member]
Debt Instrument [Line Items]
Long-term debt		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
6.50% 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
6.150% 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
5.90% 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 2014-2029 [Member]
Debt Instrument [Line Items]
Long-term debt	325	397
Iowa Finance Authority Loan, Due 2042 (4.75%) [Member]
Debt Instrument [Line Items]
Long-term debt	250	250
Other [Member]
Debt Instrument [Line Items]
Long-term debt	$ 185	$ 205