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Employee Benefit Plans - Assumptions Used for Postretirement Benefit Obligations and Postretirement Costs (Details) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2017 | Dec. 31, 2016
Retirement Benefits [Abstract] |  |
Postretirement benefit obligations, discount rate | 4.00% | 4.30%
Postretirement costs, discount rate | 4.00% | 4.30%
Health care cost trend rate for medical benefits assumed for next year (pre-65) | 7.75% | 7.50%
Health care cost trend rate for medical benefits assumed for next year (post-65) | 6.00% | 5.00%
Ultimate trend rate (pre-65) | 4.50% | 4.50%
Ultimate trend rate (post-65) | 4.50% | 4.50%
Year that the rate reaches the ultimate trend rate (pre-65) | 2030 | 2023
Year that the rate reaches the ultimate trend rate (post-65) | 2023 | 2018

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- Definition Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year, Post-65 + References No definition available. + Details
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- Definition Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year, Pre-65 + References No definition available. + Details
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- Definition Defined Benefit Plan, Ultimate Health Care Cost Trend Rate, Post-65 + References No definition available. + Details
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- Definition Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate, Post-65 + References No definition available. + Details
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- Definition Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate, Pre-65 + 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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- 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://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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