RATE MATTERS - Regulated Generating Units (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2026	Jan. 31, 2026	Mar. 31, 2026	Mar. 31, 2025
Public Utilities, General Disclosures [Line Items]
Asset Impairments and Other Related Charges			$ 31	$ 0
SOUTHWESTERN ELECTRIC POWER COMPANY
Public Utilities, General Disclosures [Line Items]
Asset Impairments and Other Related Charges	$ 31		31	$ 0
Pirkey Plant | SOUTHWESTERN ELECTRIC POWER COMPANY
Public Utilities, General Disclosures [Line Items]
Regulatory asset, net investment	172		172
Pirkey Plant | SOUTHWESTERN ELECTRIC POWER COMPANY | Texas
Public Utilities, General Disclosures [Line Items]
Net Book Value	46		46
Pirkey Plant | SOUTHWESTERN ELECTRIC POWER COMPANY | 2021 Arkansas Rate Case
Public Utilities, General Disclosures [Line Items]
Public utilities, approved recovery, amount		10 years
Public utilities, return on recovery, percent		3.00%
Northeastern Plant, Unit 3 | PUBLIC SERVICE COMPANY OF OKLAHOMA
Public Utilities, General Disclosures [Line Items]
Plant retired, amount			325
Unrecovered amount	$ 152		$ 152