Credit Losses - Gross Receivables and Related Allowances (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,704.0	$ 1,422.9
Allowance for credit losses	198.3	220.1	$ 140.0
Accounts receivable and unbilled revenues, net	1,505.7	1,202.8
Total accounts receivable, net - past due greater than 90 days	$ 86.5	$ 122.8
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	94.80%	95.50%
Amount of net accounts receivable with regulatory protections	$ 839.1
Percent of net accounts receivable with regulatory protections	55.70%
Public Utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,681.9	$ 1,373.5
Allowance for credit losses	198.3	220.1	139.9
Accounts receivable and unbilled revenues, net	1,483.6	1,153.4
Total accounts receivable, net - past due greater than 90 days	$ 86.5	$ 122.8
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	94.80%	95.50%
Wisconsin | Public Utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 1,053.1	$ 899.8
Allowance for credit losses	84.0	102.1	59.9
Accounts receivable and unbilled revenues, net	969.1	797.7
Total accounts receivable, net - past due greater than 90 days	$ 46.5	$ 84.8
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	97.60%	97.60%
Illinois | Public Utilities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 523.1	$ 393.9
Allowance for credit losses	105.5	111.6	75.9
Accounts receivable and unbilled revenues, net	417.6	282.3
Total accounts receivable, net - past due greater than 90 days	$ 36.6	$ 34.5
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	$ 105.7	$ 79.8
Allowance for credit losses	8.8	6.4	4.1
Accounts receivable and unbilled revenues, net	96.9	73.4
Total accounts receivable, net - past due greater than 90 days	$ 3.4	$ 3.5
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	$ 17.0	$ 45.0
Allowance for credit losses	0.0	0.0
Accounts receivable and unbilled revenues, net	17.0	45.0
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	$ 5.1	$ 4.4
Allowance for credit losses	0.0	0.0	$ 0.1
Accounts receivable and unbilled revenues, net	5.1	4.4
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%