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Employee Benefit Plans - Assumptions Used to Determine Projected and Accumulated Benefit Obligations of Domestic Defined Benefit Pension and Postretirement Benefit Plans (Detail) | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Pre-65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate | 7.00% | 7.00% |
Ultimate cost trend rate | 4.50% | 4.50% |
Year that the rate reaches the ultimate cost trend rate: | 2024 | 2023 | 2023
Post-65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate | 7.80% | 7.80% |
Ultimate cost trend rate | 4.50% | 4.50% |
Year that the rate reaches the ultimate cost trend rate: | 2024 | 2024 | 2024
Postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 3.40% | 3.90% |
Deferred compensation and excess benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 3.40% | 3.90% |
Annual increase in Medicare Part B premium | 6.00% | 6.00% |
Projected and accumulated benefit obligations | Pre-65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Year that the rate reaches the ultimate cost trend rate: | 2024 | 2024 |
Projected and accumulated benefit obligations | Post-65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Year that the rate reaches the ultimate cost trend rate: | 2024 | 2024 |

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- Definition Annual Increase In Medicare Part B Premium Used To Determine Projected And Accumulated Benefit Obligations For Domestic Postretirement Benefit Plans + References No definition available. + Details
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- Definition The ultimate trend rate for health care costs used to determine projected and accumulated benefit obligation. + References No definition available. + Details
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- Definition Health Care Cost Trend Rate used to Determine Projected and Accumulated Benefit Obligation + References No definition available. + Details
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- Definition The interest rate used to adjust for the time value of money for the 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=65897934&loc=d3e1928-114920 + Details
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- Definition Year the ultimate health care cost trend rate is expected to be reached, in CCYY format. + 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 (l) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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