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Benefit Plans, Weighted Average Asset Allocation by Asset Category (Details) | Dec. 31, 2017 | Dec. 31, 2016
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Weighted average asset allocations [Abstract] |  |
Weighted average asset allocation percentages, Total | 100.00% | 100.00%
Equity Securities [Member] |  |
Weighted average asset allocations [Abstract] |  |
Weighted average asset allocation percentages, Total | 56.00% | 60.20%
Fixed Income Securities [Member] |  |
Weighted average asset allocations [Abstract] |  |
Weighted average asset allocation percentages, Total | 36.20% | 32.70%
Real Estate [Member] |  |
Weighted average asset allocations [Abstract] |  |
Weighted average asset allocation percentages, Total | 0.80% | 0.70%
Other [Member] |  |
Weighted average asset allocations [Abstract] |  |
Weighted average asset allocation percentages, Total | 7.00% | 6.40%

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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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