Goodwill and Intangibles - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Goodwill
Changes to the carrying amount of goodwill		$ 0.0	$ 0.0
Goodwill		3,052.8	3,052.8
Accumulated impairment losses		0.0
Goodwill impairment loss	$ 0.0
Wisconsin
Goodwill
Goodwill		2,104.3	2,104.3
Illinois
Goodwill
Goodwill		758.7	758.7
Other States
Goodwill
Goodwill		183.2	183.2
Non-Utility Energy Infrastructure
Goodwill
Goodwill		$ 6.6	$ 6.6