Revenues (Details) - Regulated Electric [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 1,193.3	$ 1,236.7
Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	351.9	363.7
Retail \| Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	800.3	828.3
Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	41.1	44.7
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	361.0	426.0
Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	239.6	231.1
Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	3.3	12.8
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,797.2	1,906.6
Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	28.6	26.6
Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 1,825.8	$ 1,933.2

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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