Summary of Significant Accounting Policies AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Funds Used During Construction
AFUDC - Debt	$ 6.9	$ 4.9	$ 10.9
AFUDC - Equity	$ 15.2	11.4	25.1
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	$ 1.5	1.2	1.7
AFUDC - Equity	$ 3.9	3.1	4.2
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	$ 1.9	1.6	8.1
AFUDC - Equity	$ 4.6	4.1	19.5
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	$ 0.2	1.1	0.3
AFUDC - Equity	$ 0.6	3.0	0.9
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	$ 0.2	0.3	0.2
AFUDC - Equity	$ 0.6	0.9	0.5
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	$ 2.4	0.1
AFUDC - Equity	5.4	0.2
Other
Allowance for Funds Used During Construction
AFUDC - Debt	0.7	0.6	0.6
AFUDC - Equity	$ 0.1	$ 0.1	$ 0.0
Retail operations \| WE
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	8.45%
Retail operations \| WPS
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	7.72%
Retail operations \| WBS
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	7.72%
Retail operations \| WG
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	8.33%
Retail operations \| UMERC
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	6.28%
Wholesale operations \| WE
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	3.63%
Wholesale operations \| WPS
Allowance for Funds Used During Construction
Interest rate on accrued AFUDC	1.96%

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.

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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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