| Debt Outstanding (Parenthetical) (Detail) | Jun. 30, 2012 | Dec. 31, 2011 | 
|---|---|---|
| Notes, 7.34%, due in installments through May 2014 | ||
| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 7.34% | 7.34% | 
| Debt, maturity date | 2014-05 | 2014-05 | 
| Notes, 4.45%, due December 2014 | ||
| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 4.45% | 4.45% | 
| Debt, maturity date | 2014-12 | 2014-12 | 
| Notes, 6.30%, due July 2017 | ||
| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 6.30% | 6.30% | 
| Debt, maturity date | 2017-07 | 2017-07 | 
| Debentures, 6.90%, due July 2028 | ||
| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 6.90% | 6.90% | 
| Debt, maturity date | 2028-07 | 2028-07 | 
| Notes, 7.00%, due July 2037 | ||
| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 7.00% | 7.00% | 
| Debt, maturity date | 2037-07 | 2037-07 |