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Benefit Plans, Fair Values by Asset Category (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Weighted average asset allocations value [Abstract] |  |
Fair value of plan assets | $ 320.2 | $ 289.3
Equity Securities [Member] |  |
Weighted average asset allocations value [Abstract] |  |
Fair value of plan assets | 179.2 | 174.1
Fixed Income Securities [Member] |  |
Weighted average asset allocations value [Abstract] |  |
Fair value of plan assets | 116.0 | 94.7
Real Estate [Member] |  |
Weighted average asset allocations value [Abstract] |  |
Fair value of plan assets | 2.4 | 1.9
Other [Member] |  |
Weighted average asset allocations value [Abstract] |  |
Fair value of plan assets | $ 22.6 | $ 18.6

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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + 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 (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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