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Pension and Other Post-retirement Benefits Accumulated Benefit Obligations (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Asset Retirement Obligation Disclosure [Abstract] |  |
Defined Benefit Plan, Accumulated Benefit Obligation | $ 902.6 | $ 844.3

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + 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 (e) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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Namespace Prefix: | us-gaap_
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