Credit Losses - Gross Receivables and Related Allowances (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,696.7	$ 2,017.7
Allowance for credit losses	193.5	199.3	$ 198.3	$ 220.1
Accounts receivable and unbilled revenues, net	1,503.2	1,818.4
Total accounts receivable, net - past due greater than 90 days	$ 98.8	$ 106.7
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	94.50%	96.80%
Amount of net accounts receivable with regulatory protections	$ 914.6
Percent of net accounts receivable with regulatory protections	60.80%
Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,654.4	$ 1,988.0
Allowance for credit losses	193.5	199.3
Accounts receivable and unbilled revenues, net	1,460.9	1,788.7
Total accounts receivable, net - past due greater than 90 days	$ 98.8	$ 106.7
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	94.50%	96.80%
Wisconsin | Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,078.0	$ 1,199.4
Allowance for credit losses	77.4	82.0	84.0	102.1
Accounts receivable and unbilled revenues, net	1,000.6	1,117.4
Total accounts receivable, net - past due greater than 90 days	$ 51.7	$ 51.9
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	93.60%	97.00%
Illinois | Public utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 481.5	$ 624.2
Allowance for credit losses	109.7	111.0	105.5	111.6
Accounts receivable and unbilled revenues, net	371.8	513.2
Total accounts receivable, net - past due greater than 90 days	$ 45.0	$ 52.9
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	$ 94.9	$ 164.4
Allowance for credit losses	6.4	6.3	$ 8.8	$ 6.4
Accounts receivable and unbilled revenues, net	88.5	158.1
Total accounts receivable, net - past due greater than 90 days	$ 2.1	$ 1.9
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	$ 33.9	$ 25.4
Allowance for credit losses	0.0	0.0
Accounts receivable and unbilled revenues, net	33.9	25.4
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%
Corporate and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 8.4	$ 4.3
Allowance for credit losses	0.0	0.0
Accounts receivable and unbilled revenues, net	8.4	4.3
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%