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Retirement Benefit Plans (Weighted Average Asset Allocations) (Details) - Pension Plans, Defined Benefit | Dec. 31, 2017 | Dec. 31, 2016
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Hourly Employees’ Pension Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 0.00% | 0.00%
Hourly Employees’ Pension Plan | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 0.00% | 0.00%
Hourly Employees’ Pension Plan | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 0.00% | 0.00%
Hourly Employees’ Pension Plan | Short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 0.00% | 0.00%
Hourly Employees’ Pension Plan | Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 0.00% | 0.00%
Employees’ Retirement Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 100.00% | 100.00%
Employees’ Retirement Plan | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 55.00% | 54.00%
Employees’ Retirement Plan | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 38.00% | 38.00%
Employees’ Retirement Plan | Short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 2.00% | 3.00%
Employees’ Retirement Plan | Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Asset allocations as a percentage of plan assets | 5.00% | 5.00%

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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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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