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Debt Outstanding (Parenthetical) (Detail)
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Mar. 31, 2013
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Dec. 31, 2012
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| Debt Outstanding [Line Items] | ||
| Debt, maturity date | 2017-12 | |
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Notes, 7.34%, due in installments through May 2014 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 7.34% | 7.34% |
| Debt, maturity date | 2014-05 | 2014-05 |
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Notes, 4.45%, due December 2014 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 4.45% | 4.45% |
| Debt, maturity date | 2014-12 | 2014-12 |
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Notes, 6.30%, due July 2017 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 6.30% | 6.30% |
| Debt, maturity date | 2017-07 | 2017-07 |
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Notes, 3.30%, due Dec 2022 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 3.30% | 3.30% |
| Debt, maturity date | 2022-12 | 2022-12 |
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Debentures, 6.90%, Due July 2028 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 6.90% | 6.90% |
| Debt, maturity date | 2028-07 | 2028-07 |
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Notes, 7.00%, Due July 2037 [Member]
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| Debt Outstanding [Line Items] | ||
| Debt, interest rate | 7.00% | 7.00% |
| Debt, maturity date | 2037-07 | 2037-07 |