POSTRETIREMENT BENEFIT PLANS - Components of Expense (Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Non-operating	$ (102)	$ (94)	$ (306)	$ (332)
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Curtailment loss (gain)		17
Pension Plans | Principal Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	7	8	21	25
Interest cost	227	237	681	715
Expected return on plan assets	(284)	(292)	(851)	(878)
Amortization of net loss (gain)	(19)	(30)	(57)	(96)
Amortization of prior service cost (credit)	2	1	6	2
Curtailment loss (gain)	0	17	0	17
Non-operating	(74)	(67)	(221)	(240)
Net periodic expense (income)	(67)	(58)	(200)	(215)
Pension Plans | Other Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	6	6	18	18
Interest cost	50	53	150	157
Expected return on plan assets	(64)	(65)	(190)	(192)
Amortization of net loss (gain)	5	2	15	7
Amortization of prior service cost (credit)	0	(1)	0	(3)
Curtailment loss (gain)	0	0	0	0
Non-operating	(9)	(11)	(25)	(31)
Net periodic expense (income)	(3)	(5)	(7)	(13)
OPEB Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	2	2	6	6
Interest cost	14	15	41	45
Expected return on plan assets	0	0	0	0
Amortization of net loss (gain)	(15)	(16)	(45)	(48)
Amortization of prior service cost (credit)	(22)	(22)	(66)	(66)
Curtailment loss (gain)	0	0	0	0
Non-operating	(23)	(23)	(70)	(69)
Net periodic expense (income)	$ (21)	$ (21)	$ (64)	$ (63)