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Postretirement Benefit Plans - Summary of Actual Pension Plan Asset Allocation (Detail)
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12 Months Ended | |
|---|---|---|
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Dec. 31, 2012
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Dec. 31, 2011
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| Plan Asset Allocation [Line Items] | ||
| Actual benefit plan asset allocation | 100.00% | 100.00% |
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Equity securities [Member]
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| Plan Asset Allocation [Line Items] | ||
| Actual benefit plan asset allocation | 26.00% | 21.00% |
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Debt securities [Member]
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| Plan Asset Allocation [Line Items] | ||
| Actual benefit plan asset allocation | 58.00% | 64.00% |
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Insurance contracts [Member]
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| Plan Asset Allocation [Line Items] | ||
| Actual benefit plan asset allocation | 3.00% | 4.00% |
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Other [Member]
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| Plan Asset Allocation [Line Items] | ||
| Actual benefit plan asset allocation | 13.00% | 11.00% |