Regulatory Assets and Liabilities - Plant Retirements (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2019
Regulatory assets
Total regulatory assets	$ 3,306.9	$ 3,367.1
Deferred tax liabilities	4,072.5	3,909.0
Securitization
Regulatory assets
Total regulatory assets	92.4	$ 100.7
Edgewater Unit 4
Regulatory assets
Total regulatory assets	3.2
Pleasant Prairie power plant
Regulatory assets
Net book value of retired plant	575.1
Deferred unprotected tax benefits	17.5
Total regulatory assets	557.6
Deferred tax liabilities	156.7
Pleasant Prairie power plant | Securitization
Regulatory assets
Total regulatory assets			$ 100.0
Presque Isle power plant
Regulatory assets
Net book value of retired plant	163.7
Deferred unprotected tax benefits	5.2
Total regulatory assets	158.5
Deferred tax liabilities	44.4
Pulliam power plant
Regulatory assets
Total regulatory assets	$ 36.6