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Debt outstanding (Parenthetical) (Detail)
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6 Months Ended | 12 Months Ended |
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Jun. 30, 2011
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Dec. 31, 2010
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Note, 4.25%, due in installments through March 2012
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 4.25% | 4.25% |
| Debt, maturity date | March, 2012 | March, 2012 |
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Notes, 7.34%, due in installments through May 2014
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 7.34% | 7.34% |
| Debt, maturity date | May, 2014 | May, 2014 |
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Notes, 4.45%, due December 2014
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 4.45% | 4.45% |
| Debt, maturity date | December, 2014 | December, 2014 |
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Notes, 6.30%, due July 2017
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 6.30% | 6.30% |
| Debt, maturity date | July, 2017 | July, 2017 |
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Debentures, 6.90%, due July 2028
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 6.90% | 6.90% |
| Debt, maturity date | July, 2028 | July, 2028 |
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Notes, 7.00%, due July 2037
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| Debt Instrument [Line Items] | ||
| Debt, interest rate | 7.00% | 7.00% |
| Debt, maturity date | July, 2037 | July, 2037 |