Credit Losses - Gross Receivables and Related Allowances (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,832.1	$ 1,696.7
Allowance for credit losses	162.8	193.5	$ 199.3	$ 198.3
Accounts receivable and unbilled revenues, net	1,669.3	1,503.2
Total accounts receivable, net - past due greater than 90 days	$ 84.4	$ 98.8
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	93.20%	94.50%
Amount of net accounts receivable with regulatory protections	$ 1,029.0
Percent of net accounts receivable with regulatory protections	61.60%
Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,786.1	$ 1,654.4
Allowance for credit losses	162.8	193.5
Accounts receivable and unbilled revenues, net	1,623.3	1,460.9
Total accounts receivable, net - past due greater than 90 days	$ 84.4	$ 98.8
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	93.20%	94.50%
Wisconsin | Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,149.9	$ 1,078.0
Allowance for credit losses	73.6	77.4	82.0	84.0
Accounts receivable and unbilled revenues, net	1,076.3	1,000.6
Total accounts receivable, net - past due greater than 90 days	$ 51.8	$ 51.7
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	93.80%	93.60%
Illinois | Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 535.6	$ 481.5
Allowance for credit losses	83.9	109.7	111.0	105.5
Accounts receivable and unbilled revenues, net	451.7	371.8
Total accounts receivable, net - past due greater than 90 days	$ 30.1	$ 45.0
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	100.00%	100.00%
Other States | Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 100.6	$ 94.9
Allowance for credit losses	5.3	6.4	$ 6.3	$ 8.8
Accounts receivable and unbilled revenues, net	95.3	88.5
Total accounts receivable, net - past due greater than 90 days	$ 2.5	$ 2.1
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	0.00%	0.00%
Non-Utility Energy Infrastructure
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 40.0	$ 33.9
Allowance for credit losses	0.0	0.0
Accounts receivable and unbilled revenues, net	40.0	33.9
Total accounts receivable, net - past due greater than 90 days	$ 0.0	$ 0.0
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	0.00%	0.00%
Corporate and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 6.0	$ 8.4
Allowance for credit losses	0.0	0.0
Accounts receivable and unbilled revenues, net	6.0	8.4
Total accounts receivable, net - past due greater than 90 days	$ 0.0	$ 0.0
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	0.00%	0.00%