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Pension and Other Postretirement Benefit Plans - Summary of Health Care Cost Trend Rate Assumptions for Other Postretirement Benefit Plans (Detail) (Other Postretirement Benefit Plans, Defined Benefit [Member])
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12 Months Ended | |
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Dec. 31, 2013
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Dec. 31, 2012
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Other Postretirement Benefit Plans, Defined Benefit [Member]
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| Defined Benefit Plan Disclosure [Line Items] | ||
| Health care cost trend rate assumed for next year | 7.10% | 7.50% |
| Rate to which the cost trend rate is assumed to decline | 4.60% | 5.00% |
| Year that the trend rate reaches the ultimate trend rate | 2027 | 2018 |