GOODWILL AND INTANGIBLES - GOODWILL (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)
Goodwill balance by segment
Changes to the carrying amount of goodwill		$ 0.0
Goodwill	$ 3,052.8	3,052.8
Accumulated impairment losses	0.0	0.0
Goodwill impairment loss	0.0
Wisconsin
Goodwill balance by segment
Goodwill	2,104.3	2,104.3
Illinois
Goodwill balance by segment
Goodwill	758.7	758.7
Other States
Goodwill balance by segment
Goodwill	183.2	183.2
Non-Utility Energy Infrastructure
Goodwill balance by segment
Goodwill	$ 6.6	$ 6.6

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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