LEASES - FUTURE MINIMUM LEASE PAYMENTS (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Finance leases
Long-term lease finance liabilities	$ 361.8	$ 303.3
WECI | Hardin Solar III Energy Center
Operating leases
Six months ended December 31, 2025	0.4
2026	1.5
2027	1.5
2028	1.5
2029	1.6
2030	1.6
Thereafter	110.2
Total minimum lease payments	118.3
Less: interest	(88.9)
Operating lease obligation	29.4
Less: short-term lease liabilities	0.0
Long-term lease operating liabilities	29.4
WE and WPS | High Noon
Finance leases
Six Months Ended December 31, 2025	2.7
2026	1.4
2027	1.8
2028	3.6
2029	3.7
2030	3.8
Thereafter	290.8
Total minimum lease payments	307.8
Less: Interest	(241.2)
Present value of minimum lease payments	66.6
Less: short-term lease liabilities	0.0
Long-term lease finance liabilities	$ 66.6