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Retirement Benefits Plans (Narrative) (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2011 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Company's pretax income and the aggregate compensation levels of participating employees |  | $ 6.6 | $ 6.8 | $ 6.5
Postretirement benefit plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Years of service, less than | 10 years |  |  |
Health care cost trend assumption increased health care cost trend rates (as a percent) |  | 6.25% | 6.25% |
Health care cost trend assumption increased health care cost trend rates (as a percent) |  | 5.00% |  |

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- Definition Defined benefit plan assumptions used calculating benefit obligation health care cost trend rate. + References No definition available. + Details
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- Definition Defined Benefit Plan, Years of Service + References No definition available. + Details
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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 Ultimate trend rate for health care cost for defined benefit postretirement plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Details
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