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Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | $ 2,660.0 | $ 2,795.6
Overrecovered Gas And Fuel Costs |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | 32.0 | 27.6
Cost Of Removal |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | 1,076.0 | 1,096.8
Regulatory Effects Of Accounting For Income Taxes |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | 1,428.3 | 1,563.4
Other Postretirement Costs |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | 62.7 | 59.0
Other Liabilities |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities | $ 61.0 | $ 48.8

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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