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Retirement Plans - Schedule of Weighted-Average Assumptions Used to Determine Net Periodic Cost (Detail) - Net Periodic Cost [Member] | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Net Periodic Benefit Cost Assumptions [Line Items] |  |  |
Discount rate | 3.37% | 3.74% | 3.88%
Health care cost trend: Initial | 6.00% | 6.00% | 6.25%
Health care cost trend: Ultimate | 4.75% | 4.75% | 4.75%
Year ultimate reached | 2023 | 2022 | 2022
Corridor | 10.00% | 10.00% | 10.00%
Recognition period for gains and losses | 12 years 1 month | 11 years | 11 years

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- Definition Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Recognized Period + References No definition available. + Details
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- Definition Defined Benefit Plan Corridor Rate + References No definition available. + Details
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- Definition Defined Benefit Plan Initial Health Care Cost Trend Rate + References No definition available. + Details
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- Definition Net Periodic Benefit Cost Assumptions [Line Items] + 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 net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Ultimate trend rate for health care cost for defined benefit postretirement plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Year ultimate health care cost trend rate is expected to be reached, in CCYY format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Details
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