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Fair Value of Postretirement Assets (Parenthetical) (Detail)
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Dec. 31, 2011
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| Defined Benefit Plan Disclosure [Line Items] | |
| Hedge funds, minimum number of days notice prior to redemption | 30 days |
| Hedge funds, maximum number of days notice prior to redemption | 90 days |
| X | ||||||||||
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- Definition
Redemption Notice Period, Lower Limit No definition available.
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| X | ||||||||||
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- Definition
Redemption Notice Period Upper Limit No definition available.
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| X | ||||||||||
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- Details
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