Regulatory Assets and Liabilities - Plant Retirements (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	May 31, 2021
Regulatory assets
Total regulatory assets	$ 3,378.7	$ 3,274.7
Regulatory liability	4,003.3	3,745.2
Deferred tax liabilities	4,545.2	4,198.0
Securitization
Regulatory assets
Total regulatory assets	76.5	$ 85.9
Edgewater Generating Station unit 4
Regulatory assets
Total regulatory assets	1.0
Oak Creek power plant units 5 and 6
Regulatory assets
Total regulatory assets	75.3
Regulatory liability	43.8
Deferred tax liabilities	8.6
Pleasant Prairie power plant
Regulatory assets
Net book value of retired plant	506.8
Deferred unprotected tax benefits	15.4
Total regulatory assets	491.4
Deferred tax liabilities	138.0
Pleasant Prairie power plant | Securitization
Regulatory assets
Total regulatory assets			$ 100.0
Presque Isle power plant
Regulatory assets
Net book value of retired plant	142.6
Deferred unprotected tax benefits	4.4
Total regulatory assets	138.2
Deferred tax liabilities	38.7
Pulliam power plant
Regulatory assets
Total regulatory assets	$ 29.3