PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Net Periodic Benefit Cost and Assumptions used to Estimate our Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	1 Months Ended	11 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.40%	4.30%
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 36	$ 32	$ 37
Interest cost			139	160	236
Expected return on plan assets			(234)	(223)	(399)
Amortization of actuarial loss			122	112	225
Amortization of prior service cost (credit)			3	4	3
Settlement charges			253	455	200
Net periodic benefit cost			$ 319	$ 540	$ 302
Expected return on assets			6.50%	7.00%	8.00%
Lump sum or installment distributions election			60.00%	60.00%	60.00%
Pension | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.10%	3.70%	3.50%
Rate of compensation increase			2.00%	2.00%	2.00%
Pension | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.40%	4.40%	3.70%
Rate of compensation increase			13.00%	13.00%	13.00%
Other Post-employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 0	$ 0	$ 0
Interest cost			4	6	7
Expected return on plan assets			0	0	0
Amortization of actuarial loss			4	7	8
Amortization of prior service cost (credit)			(1)	(5)	(8)
Settlement charges			0	0	0
Net periodic benefit cost			$ 7	$ 8	$ 7
Discount rate			3.00%
Other Post-employment Benefits | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate				3.70%	3.40%
Weighted health care cost trend rate assumed		4.50%	4.50%	4.50%	4.50%
Other Post-employment Benefits | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate				4.20%	3.50%
Weighted health care cost trend rate assumed		7.80%	7.30%	7.80%	7.80%