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Income Taxes (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
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Jun. 30, 2020 | Dec. 31, 2017
Income Tax [Line Items] |  |
Reduction in net deferred income tax liabilities |  | $ 1,140.0
Amortization of an excess deferred tax liability | $ 13.5 |
Regulatory liability, amortization period | 28 years 6 months |
Domestic Tax Authority |  |
Income Tax [Line Items] |  |
Amortization of an excess deferred tax liability | $ 14.0 |

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- Definition [Line Items] for Income Tax [Table] + References No definition available. + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other deductions. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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- Definition Amortization period for the recovery of regulatory liability, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Amount of income tax benefit for remeasurement of deferred tax liability from change in tax rate pursuant to Tax Cuts and Jobs Act. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 + Details
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