PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost			$ 139	$ 184	$ 195
Interest cost			428	273	226
Expected return on plan assets			(570)	(657)	(652)
Amortization of prior service costs (credits)			2	2	3
Special termination costs			21	0	0
Pension & OPEB mark-to-market	$ 137	$ 59	108	(98)	(253)
Net periodic benefit costs (credits)			128	(296)	(481)
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost			2	3	4
Interest cost			21	11	11
Expected return on plan assets			(31)	(39)	(36)
Amortization of prior service costs (credits)			(8)	(11)	(17)
Special termination costs			8	0	0
Pension & OPEB mark-to-market			(30)	26	(129)
Net periodic benefit costs (credits)			$ (38)	$ (10)	$ (167)