POSTRETIREMENT BENEFIT PLANS - Components of Expense (Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Non-operating	$ (101)	$ (123)	$ (204)	$ (238)
Pension Plans | Principal Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	7	9	14	17
Interest cost	227	238	454	478
Expected return on plan assets	(284)	(293)	(567)	(586)
Amortization of net loss (gain)	(19)	(35)	(38)	(66)
Amortization of prior service cost (credit)	2	0	4	0
Non-operating	(74)	(90)	(147)	(174)
Net periodic expense (income)	(67)	(81)	(133)	(157)
Pension Plans | Other Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	6	6	12	12
Interest cost	50	53	100	105
Expected return on plan assets	(63)	(64)	(126)	(127)
Amortization of net loss (gain)	5	3	10	5
Amortization of prior service cost (credit)	0	(1)	0	(2)
Non-operating	(8)	(10)	(16)	(20)
Net periodic expense (income)	(2)	(4)	(4)	(8)
OPEB Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost – Operating	2	2	4	4
Interest cost	14	15	27	30
Expected return on plan assets	0	0	0	0
Amortization of net loss (gain)	(15)	(16)	(30)	(32)
Amortization of prior service cost (credit)	(22)	(22)	(44)	(44)
Non-operating	(23)	(23)	(47)	(46)
Net periodic expense (income)	$ (21)	$ (21)	$ (43)	$ (42)