FAIR VALUE MEASUREMENTS - Changes in Fair Value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	$ 165.6	$ 139.4
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	92.0	46.9
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	18.8	11.3
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	5.5	0.6
Settlements	(167.8)	(96.6)
Transfers into Level 3	0.7	4.6
Transfers out of Level 3	0.8	2.1
Changes in Fair Value Allocated to Regulated Jurisdiction	7.2	10.8
Ending Balance	122.8	119.1
APCo
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	35.2	22.4
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	40.0	9.2
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	0.0	0.0
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	0.0	0.0
Settlements	(66.5)	(26.8)
Transfers into Level 3	0.0	0.0
Transfers out of Level 3	0.0	0.0
Changes in Fair Value Allocated to Regulated Jurisdiction	(0.7)	(0.8)
Ending Balance	8.0	4.0
I&M
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	6.4	2.8
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	8.9	3.2
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	0.0	0.0
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	0.0	0.0
Settlements	(12.4)	(4.8)
Transfers into Level 3	0.0	0.0
Transfers out of Level 3	0.0	0.0
Changes in Fair Value Allocated to Regulated Jurisdiction	1.0	(0.2)
Ending Balance	3.9	1.0
OPCo
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	(47.5)	(50.6)
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	(0.1)	(0.4)
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	0.0	0.0
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	0.0	0.0
Settlements	2.1	2.6
Transfers into Level 3	0.0	0.0
Transfers out of Level 3	0.0	0.0
Changes in Fair Value Allocated to Regulated Jurisdiction	(5.7)	7.4
Ending Balance	(51.2)	(41.0)
PSO
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	20.0	18.6
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	16.9	18.5
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	0.0	0.0
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	0.0	0.0
Settlements	(28.1)	(31.3)
Transfers into Level 3	0.0	0.0
Transfers out of Level 3	0.0	0.0
Changes in Fair Value Allocated to Regulated Jurisdiction	6.6	1.9
Ending Balance	15.4	7.7
SWEPCo
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	17.5	11.1
Realized Gain (Loss) Included in Net Income (or Changes in Net Assets)	20.8	14.7
Unrealized Gain (Loss) Included in Net Income (or Changes in Net Assets) Relating to Assets Still Held at the Reporting Date	0.0	0.0
Realized and Unrealized Gains (Losses) Included in Other Comprehensive Income	0.0	0.0
Settlements	(31.3)	(23.6)
Transfers into Level 3	0.0	0.0
Transfers out of Level 3	0.0	0.5
Changes in Fair Value Allocated to Regulated Jurisdiction	6.1	2.6
Ending Balance	$ 13.1	$ 5.3