PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Change in benefit obligation:
Benefit obligation as of January 1	$ 8,828	$ 11,479
Service cost	139	184	$ 195
Interest cost	428	273	226
Plan participants’ contributions	0	0
Special termination benefits	21	0
Medicare retiree drug subsidy	0	0
Lift-out transaction	(719)	0
Actuarial loss (gain)	256	(2,515)
Benefits paid	(590)	(593)
Benefit obligation as of December 31	8,363	8,828	11,479
Change in fair value of plan assets:
Fair value of plan assets as of January 1	6,693	9,020
Actual return on plan assets	682	(1,760)
Lift-out transaction	(683)	0
Company contributions	777	26
Plan participants’ contributions	0	0
Benefits paid	(590)	(593)
Fair value of plan assets as of December 31	6,879	6,693	9,020
Funded Status:
Funded Status (Net liability as of December 31)	(1,484)	(2,135)
Accumulated benefit obligation	7,324	8,500
Amounts Recognized in AOCI:
Prior service cost (credit)	4	6
Pension | Qualified plan
Funded Status:
Funded Status (Net liability as of December 31)	(1,090)	(1,734)
Pension | Non-qualified plans
Funded Status:
Funded Status (Net liability as of December 31)	(394)	(401)
OPEB
Change in benefit obligation:
Benefit obligation as of January 1	439	549
Service cost	2	3	4
Interest cost	21	11	11
Plan participants’ contributions	4	3
Special termination benefits	8	0
Medicare retiree drug subsidy	0	1
Lift-out transaction	0	0
Actuarial loss (gain)	8	(83)
Benefits paid	(41)	(45)
Benefit obligation as of December 31	441	439	549
Change in fair value of plan assets:
Fair value of plan assets as of January 1	460	548
Actual return on plan assets	69	(70)
Lift-out transaction	0	0
Company contributions	24	24
Plan participants’ contributions	4	3
Benefits paid	(41)	(45)
Fair value of plan assets as of December 31	516	460	$ 548
Funded Status:
Funded Status (Net liability as of December 31)	75	21
Accumulated benefit obligation	0	0
Amounts Recognized in AOCI:
Prior service cost (credit)	(1)	(10)
OPEB | Qualified plan
Funded Status:
Funded Status (Net liability as of December 31)	0	0
OPEB | Non-qualified plans
Funded Status:
Funded Status (Net liability as of December 31)	$ 0	$ 0