Schedule I - Cash Dividends Received from Subsidiaries (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ATC Holding LLC
Notes to parent company financial statements
Return of capital from subsidiaries	$ 19.6	$ 220.6	$ 290.2
WECI
Notes to parent company financial statements
Return of capital from subsidiaries	583.2	116.7
WEC Energy Group
Notes to parent company financial statements
Cash dividends received from subsidiaries	898.1	735.3	688.9
Return of capital from subsidiaries	602.8	337.3	290.2
WEC Energy Group \| WE
Notes to parent company financial statements
Cash dividends received from subsidiaries	395.0	360.0	310.0
WEC Energy Group \| We Power
Notes to parent company financial statements
Cash dividends received from subsidiaries	240.9	192.5	223.0
WEC Energy Group \| ATC Holding LLC
Notes to parent company financial statements
Cash dividends received from subsidiaries	112.6	87.4	105.8
WEC Energy Group \| WG
Notes to parent company financial statements
Cash dividends received from subsidiaries	70.0	60.0	50.0
WEC Energy Group \| UMERC
Notes to parent company financial statements
Cash dividends received from subsidiaries	46.0	10.0	0.0
WEC Energy Group \| WECI
Notes to parent company financial statements
Cash dividends received from subsidiaries	33.6	25.4	0.0
WEC Energy Group \| Wisvest
Notes to parent company financial statements
Cash dividends received from subsidiaries	$ 0.0	$ 0.0	$ 0.1

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This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(b))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21D
-URI http://asc.fasb.org/extlink&oid=121586364&loc=SL94080555-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585

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