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Employee Bargaining Agreements and Benefit Plans - Assumption Rates Used for Benefit Obligations (Detail) | Dec. 31, 2017 | Dec. 31, 2016
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Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract] |  |
Discount rate: | 2.50% | 2.70%

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- References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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