Leases - Finance and Operating Lease Right of Use Assets and Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Leases
Operating lease right of use assets	$ 32.1	$ 32.0
Finance lease right of use assets	281.3	133.8
Current operating lease liabilities	4.3	4.7
Long-term operating lease liabilities	37.5	38.8
Current finance lease liabilities	0.2
Long-term finance lease liabilities	303.3	145.9
Accumulated amortization	$ 10.0	$ 6.1
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 $11,611.9 and $11,073.1, respectively	Property, plant, and equipment, net of accumulated depreciation and amortization of $11,611.9 and $11,073.1, 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]	Other	Other
Land lease - utility solar generation
Leases
Finance lease right of use assets	$ 235.8	$ 132.7
Current finance lease liabilities	0.0
Long-term finance lease liabilities	257.9	144.8
Land lease - non-utility energy infrastructure solar generation
Leases
Finance lease right of use assets	43.5	0.0
Current finance lease liabilities	0.0
Long-term finance lease liabilities	43.8	0.0
Other
Leases
Finance lease right of use assets	2.0	1.1
Current finance lease liabilities	0.2	0.0
Long-term finance lease liabilities	$ 1.6	$ 1.1