REGULATORY MATTERS - Transmission ROE Incentive (Details) - FERC $ in Millions				9 Months Ended	12 Months Ended
	Jul. 27, 2026	Jan. 17, 2025	Feb. 24, 2022	Sep. 30, 2026 USD ($)	Dec. 31, 2024 USD ($)
Transmission Related Vegetation Management Programs
Regulatory Matters [Line Items]
Basis point adder associated with RTO membership			0.0050
Transmission ROE Incentive
Regulatory Matters [Line Items]
Basis point adder associated with RTO membership		0.0050
Transmission ROE Incentive \| ATSI
Regulatory Matters [Line Items]
Pre-tax charge with interest recorded					$ 46
Request to remove basis point adder	0.0050
Limited refund period	15 months
Estimated refund obligation				$ 51
Transmission ROE Incentive \| Income Statement Location [Axis]: us-gaap:OtherNonoperatingIncomeExpense
Regulatory Matters [Line Items]
Pre-tax charge with interest recorded					4
Transmission ROE Incentive \| Revenues from affiliates \| Income Statement Location [Axis]: us-gaap:Revenues
Regulatory Matters [Line Items]
Pre-tax charge with interest recorded					$ 42