Summary of Significant Accounting Policies AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Funds Used During Construction
AFUDC - Debt	$ 8.0	$ 5.9	$ 6.9
AFUDC – Equity	$ 20.9	14.4	15.2
WE
Allowance for Funds Used During Construction
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation	50.00%
AFUDC - Debt	$ 2.6	1.5	1.5
AFUDC – Equity	$ 7.0	3.7	3.9
WPS
Allowance for Funds Used During Construction
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation	50.00%
AFUDC - Debt	$ 4.6	2.4	1.9
AFUDC – Equity	$ 11.8	5.7	4.6
WG
Allowance for Funds Used During Construction
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation	50.00%
AFUDC - Debt	$ 0.6	0.5	0.2
AFUDC – Equity	$ 1.6	1.3	0.6
UMERC
Allowance for Funds Used During Construction
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation	50.00%
AFUDC - Debt	$ 0.0	1.3	2.4
AFUDC – Equity	$ 0.1	3.3	5.4
WBS
Allowance for Funds Used During Construction
Percentage of retail jurisdictional construction work in progress expenditure subject to public utilities allowance for funds used during construction calculation	50.00%
AFUDC - Debt	$ 0.1	0.1	0.2
AFUDC – Equity	0.2	0.2	0.6
Other
Allowance for Funds Used During Construction
AFUDC - Debt	0.1	0.1	0.7
AFUDC – Equity	$ 0.2	$ 0.2	$ 0.1
Retail operations \| WE
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	8.68%
Retail operations \| WPS
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	7.55%
Retail operations \| WG
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	8.32%
Retail operations \| UMERC
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	6.28%
Retail operations \| WBS
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	7.55%
Wholesale operations \| WE
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	5.39%
Wholesale operations \| WPS
Allowance for Funds Used During Construction
Average AFUDC rate (as a percent)	5.59%

The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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Amount capitalized of allowance for funds used during construction.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

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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.

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Represents the percentage of retail jurisdictional construction work in progress expenditures subject to the AFUDC calculation.

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