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Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 2,065.5	$ 2,512.2
Regulatory Liability, Current	161.3	160.2
Regulatory Liability, Noncurrent	1,904.2	2,352.0
Overrecovered Gas And Fuel Costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	47.8	42.6
Cost Of Removal
Regulatory Liabilities [Line Items]
Regulatory Liabilities	775.2	1,047.5
Regulatory Effects Of Accounting For Income Taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,105.1	1,307.0
Other Postretirement Costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	69.5	64.7
Other Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 67.9	$ 50.4

X

- 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

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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.

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current 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

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent 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 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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