PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension
Change in benefit obligation:
Benefit obligation as of January 1	$ 11,935	$ 11,050
Service cost	195	194	$ 193
Interest cost	226	287	373
Plan participants’ contributions	0	0
Plan amendments	0	9
Medicare retiree drug subsidy	0	0
Actuarial loss (gain)	(280)	1,011
Benefits paid	(597)	(616)
Benefit obligation as of December 31	11,479	11,935	11,050
Change in fair value of plan assets:
Fair value of plan assets as of January 1	8,968	8,395
Actual return on plan assets	625	1,165
Company contributions	24	24
Plan participants’ contributions	0	0
Benefits paid	(597)	(616)
Fair value of plan assets as of December 31	9,020	8,968	8,395
Funded Status:
Funded Status (Net liability as of December 31)	(2,459)	(2,967)
Accumulated benefit obligation	10,927	11,376
Amounts Recognized in AOCI:
Prior service cost (credit)	$ 9	$ 12
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.02%	2.67%
Rate of compensation increase	4.10%	4.10%
Cash balance weighted average interest crediting rate	2.57%	2.57%
Pension | Qualified plan
Funded Status:
Funded Status (Net liability as of December 31)	$ (1,974)	$ (2,500)
Pension | Non-qualified plans
Funded Status:
Funded Status (Net liability as of December 31)	(485)	(467)
OPEB
Change in benefit obligation:
Benefit obligation as of January 1	676	654
Service cost	4	4	3
Interest cost	11	15	22
Plan participants’ contributions	4	4
Plan amendments	0	0
Medicare retiree drug subsidy	1	1
Actuarial loss (gain)	(101)	41
Benefits paid	(46)	(43)
Benefit obligation as of December 31	549	676	654
Change in fair value of plan assets:
Fair value of plan assets as of January 1	502	458
Actual return on plan assets	64	60
Company contributions	24	23
Plan participants’ contributions	4	4
Benefits paid	(46)	(43)
Fair value of plan assets as of December 31	548	502	$ 458
Funded Status:
Funded Status (Net liability as of December 31)	(1)	(174)
Accumulated benefit obligation	0	0
Amounts Recognized in AOCI:
Prior service cost (credit)	$ (21)	$ (39)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.84%	2.45%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%	4.50%
OPEB | Pre Medicare
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Health care cost trend rate assumed (pre/post-Medicare)	5.75%	6.00%
OPEB | Post Medicare
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Health care cost trend rate assumed (pre/post-Medicare)	5.25%	5.50%
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