FINANCING ACTIVITIES - Schedule of Accounts Receivable and Accrued Unbilled Revenues (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
APCo
Short-Term Debt [Line Items]
Accounts receivable and accrued unbilled revenues	$ 183.0	$ 192.7
I&M
Short-Term Debt [Line Items]
Accounts receivable and accrued unbilled revenues	185.0	160.5
OPCo
Short-Term Debt [Line Items]
Accounts receivable and accrued unbilled revenues	490.9	470.7
PSO
Short-Term Debt [Line Items]
Accounts receivable and accrued unbilled revenues	202.5	111.4
SWEPCo
Short-Term Debt [Line Items]
Accounts receivable and accrued unbilled revenues	$ 200.3	$ 153.5