| Debt Outstanding (Parenthetical) (Detail) | Dec. 31, 2012
 Notes, 7.34%, due in installments through May 2014 | Dec. 31, 2011
 Notes, 7.34%, due in installments through May 2014 | Dec. 31, 2010
 Notes, 7.34%, due in installments through May 2014 | May 31, 2007
 Notes, 7.34%, due in installments through May 2014 | Dec. 31, 2012
 Notes, 4.45%, due December 2014 | Dec. 31, 2011
 Notes, 4.45%, due December 2014 | Dec. 31, 2010
 Notes, 4.45%, due December 2014 | Nov. 04, 2009
 Notes, 4.45%, due December 2014 | Dec. 31, 2012
 Notes, 6.30%, due July 2017 | Dec. 31, 2011
 Notes, 6.30%, due July 2017 | Dec. 31, 2010
 Notes, 6.30%, due July 2017 | Jun. 28, 2007
 Notes, 6.30%, due July 2017 | Dec. 31, 2012
 Notes, 3.30%, due Dec 2022 | Dec. 17, 2012
 Notes, 3.30%, due Dec 2022 | Dec. 31, 2011
 Notes, 3.30%, due Dec 2022 | Dec. 31, 2012
 Debentures, 6.90%, due July 2028 | Dec. 31, 2011
 Debentures, 6.90%, due July 2028 | Dec. 31, 2010
 Debentures, 6.90%, due July 2028 | Dec. 31, 2012
 Notes, 7.00%, due July 2037 | Dec. 31, 2011
 Notes, 7.00%, due July 2037 | Dec. 31, 2010
 Notes, 7.00%, due July 2037 | Jun. 28, 2007
 Notes, 7.00%, due July 2037 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Debt Instrument [Line Items] | ||||||||||||||||||||||
| Debt, interest rate | 7.34% | 7.34% | 7.34% | 7.34% | 4.45% | 4.45% | 4.45% | 4.45% | 6.30% | 6.30% | 6.30% | 6.30% | 3.30% | 3.30% | 3.30% | 6.90% | 6.90% | 6.90% | 7.00% | 7.00% | 7.00% | 7.00% | 
| Debt, maturity date | 2014-05 | 2014-05 | 2014-05 | 2014-12 | 2014-12 | 2014-12 | 2017-07 | 2017-07 | 2017-07 | 2022-12 | 2012-12 | 2028-07 | 2028-07 | 2028-07 | 2037-07 | 2037-07 | 2037-07 |