Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Total Assets	$ 1,930.5	$ 2,239.6
Regulatory Assets, Current	135.7	225.7
Regulatory Assets, Noncurrent	1,794.8	2,013.9
Unrecognized Pension Benefit And Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Assets	583.3	739.1
Other Postretirement Costs
Regulatory Assets [Line Items]
Total Assets	72.4	91.3
Environmental Costs
Regulatory Assets [Line Items]
Total Assets	56.6	73.4
Regulatory Effects Of Accounting For Income Taxes
Regulatory Assets [Line Items]
Total Assets	194.5	234.0
Underrecovered Gas And Fuel Costs
Regulatory Assets [Line Items]
Total Assets	8.0	3.9
Depreciation
Regulatory Assets [Line Items]
Total Assets	192.6	210.7
Post-In Service Carrying Charges
Regulatory Assets [Line Items]
Total Assets	228.6	219.8
Safety Activity Costs
Regulatory Assets [Line Items]
Total Assets	146.0	118.6
DSM Program
Regulatory Assets [Line Items]
Total Assets	37.8	50.1
Bailly Generating Station [Member]
Regulatory Assets [Line Items]
Total Assets	204.7	221.8
Deferred Derivative Gain (Loss)
Regulatory Assets [Line Items]
Total Assets	54.7	76.4
Deferred Property Taxes
Regulatory Assets [Line Items]
Total Assets	62.9	60.3
Other Assets
Regulatory Assets [Line Items]
Total Assets	$ 88.4	$ 140.2

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.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets 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 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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