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Pensions and Other Postretirement Benefits - Assumed Health Care Cost Trend Rates (Detail)
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12 Months Ended | ||
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Aug. 31, 2012
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Aug. 31, 2011
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Aug. 31, 2010
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| Compensation And Retirement Disclosure [Abstract] | |||
| Current health care trend assumption | 8.00% | 8.00% | 8.00% |
| Ultimate health care trend rate | 4.50% | 4.50% | 4.50% |
| Year ultimate health care trend is reached | 2030 | 2029 | 2028 |