PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Narrative (Details) $ in Millions		1 Months Ended	3 Months Ended		8 Months Ended	12 Months Ended
	May 12, 2023 USD ($)	Dec. 31, 2023 USD ($) numberOfEmployee	Dec. 31, 2023 USD ($) numberOfEmployee	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) numberOfEmployee	Dec. 31, 2023 USD ($) numberOfEmployee	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 09, 2023 employee
Defined Benefit Plan Disclosure [Line Items]
Percent of eligible employees that accepted the voluntary retirement program									0.65
Number of employees | employee									450
Number of separated employees | employee									90
Defined benefit plan, assumptions used calculating benefit obligation, increase (decrease) in discount rate			0.11%	0.29%
Pension
Defined Benefit Plan Disclosure [Line Items]
Voluntary cash contribution	$ 750
Weighted-average discount rate					8.00%
Pension & OPEB mark-to-market			$ 137	$ 59		$ 108	$ (98)	$ (253)
Expected future contributions		$ 260	$ 260		$ 260	$ 260
Defined benefit plan, number of covered employees by plan | numberOfEmployee		1,900	1,900		1,900	1,900
Defined benefit plan, plan assets pre tax gain		$ 36
Pension | Banner Life Insurance Company and Reinsurance Group of America
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, increase (decrease) for assets transferred to (from) plan		683
Plan amendments		$ 719
OPEB
Defined Benefit Plan Disclosure [Line Items]
Pension & OPEB mark-to-market						$ (30)	26	(129)
OPEB | Regulated Transmission
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment, net of capitalized amounts						$ 36	$ 15	$ (31)