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Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Reserve For Accounts Receivable [Member] |  |  |  |
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |
Beginning Balance |  | $ 18.3 | $ 23.3 | $ 20.3
Valuation Allowances and Reserves, Charged to Cost and Expense |  | 20.2 | 14.8 | 19.7
Valuation Allowances and Reserves, Charged to Other Accounts | [1] | 43.7 | 39.1 | 48.5
Deductions for Purposes for which Reserves were Created |  | 61.1 | 58.9 | 65.2
Ending Balance |  | 21.1 | 18.3 | 23.3
Reserve For Other Investments [Member] |  |  |  |
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |
Beginning Balance |  | 3.0 | 3.0 | 3.0
Valuation Allowances and Reserves, Charged to Cost and Expense |  | 0.0 | 0.0 | 0.0
Valuation Allowances and Reserves, Charged to Other Accounts | [1] | 0.0 | 0.0 | 0.0
Deductions for Purposes for which Reserves were Created |  | 0.0 | 0.0 | 0.0
Ending Balance |  | $ 3.0 | $ 3.0 | $ 3.0
[1] | Charged to Other Accounts reflects the deferral of bad debt expense to a regulatory asset.

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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 Amount of valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Amount of increase in valuation and qualifying accounts and reserves from charge to cost and expense. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Amount of increase in valuation and qualifying accounts and reserves from charge to accounts other than cost and expense. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Amount of decrease in valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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