FINANCING ACTIVITIES - Long-term Debt Subsequent Events (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 29, 2025	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Total Issuances		$ 6,300.0
Principal Amount Paid		2,803.8	$ 1,969.1
I&M
Debt Instrument [Line Items]
Principal Amount Paid		269.9	$ 76.1
Notes Payable | I&M
Debt Instrument [Line Items]
Total Issuances		100.0
Notes Payable | I&M | Subsequent Event
Debt Instrument [Line Items]
Total Issuances	$ 103.0
Principal Amount Paid	8.0
Other Long-term Debt | Transource Energy
Debt Instrument [Line Items]
Total Issuances		$ 36.6
Other Long-term Debt | Transource Energy | Subsequent Event
Debt Instrument [Line Items]
Total Issuances	$ 4.0