Leases - Finance and Operating Lease Right of Use Assets and Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Leases
Operating lease right of use assets	$ 15.7	$ 19.5
Finance lease right of use assets	175.3	124.0
Current operating lease liabilities	4.0	3.7
Long-term operating lease liabilities	25.4	29.1
Current finance lease liabilities	72.7
Long-term finance lease liabilities	110.5	51.3
Accumulated amortization	$ 146.3	$ 139.7
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other	Other
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property, plant, and equipment, net of accumulated depreciation and amortization of $10,383.8 and $9,889.3, respectively	Property, plant, and equipment, net of accumulated depreciation and amortization of $10,383.8 and $9,889.3, respectively
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other	Other
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other	Other
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Current portion of long-term debt (December 31, 2022 and December 31, 2021 include $8.9 and $8.8, respectively, related to WEPCo Environmental Trust)	Current portion of long-term debt (December 31, 2022 and December 31, 2021 include $8.9 and $8.8, respectively, related to WEPCo Environmental Trust)
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt (December 31, 2022 and December 31, 2021 include $94.1 and $102.7, respectively, related to WEPCo Environmental Trust)	Long-term debt (December 31, 2022 and December 31, 2021 include $94.1 and $102.7, respectively, related to WEPCo Environmental Trust)
Power purchase commitment
Leases
Finance lease right of use assets	$ 71.8	$ 76.7
Current finance lease liabilities	72.7	78.4
Long-term finance lease liabilities	0.0
Land lease - utility solar generation
Leases
Finance lease right of use assets	102.4	47.0
Current finance lease liabilities	0.0
Long-term finance lease liabilities	109.3	51.0
Other
Leases
Finance lease right of use assets	1.1	0.3
Current finance lease liabilities	0.0
Long-term finance lease liabilities	$ 1.2	$ 0.3