PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Funded Status of Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at beginning of year	$ 4,260	$ 5,263
Service cost	36	32	$ 37
Interest cost	139	160	236
Actuarial (gains) losses	540	510
Plan participants’ contributions	0	0
Benefits paid, including lump sum and annuity transfers	(1,025)	(1,745)
Other, including foreign currency translation	21	40
Projected benefit obligation at end of year	3,971	4,260	5,263
Fair value of plan assets at beginning of year (estimated)	3,719	4,930
Actual return on plan assets(2)	490	465
Employer contributions and benefit payments	21	30
Plan participants’ contributions	0	0
Benefits paid, including lump sum and annuity transfers	(1,025)	(1,745)	(664)
Other, including foreign currency translation	25	39
Fair value of plan assets at end of year (estimated)	3,230	3,719	4,930
Noncurrent assets	58	47
Current liabilities	(17)	(19)
Noncurrent liabilities	(782)	(569)
Funded status	(741)	(541)
Accumulated benefit obligation at end of year	$ 3,855	$ 4,166
Discount rate	2.50%
Lump sum or installment distributions election	60.00%	60.00%
Pension | U.S.
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.50%	3.40%
Pension | Canada
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.50%	3.10%
Pension | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.10%
Rate of compensation increase	2.00%	2.00%
Pension | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.40%
Rate of compensation increase	13.00%	13.00%
Other Post-employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at beginning of year	$ 151	$ 166
Service cost	0	0	0
Interest cost	4	6	7
Actuarial (gains) losses	5	(8)
Plan participants’ contributions	2	2
Benefits paid, including lump sum and annuity transfers	(14)	(17)
Other, including foreign currency translation	1	2
Projected benefit obligation at end of year	149	151	166
Fair value of plan assets at beginning of year (estimated)	19	18
Actual return on plan assets(2)	0	1
Employer contributions and benefit payments	8	15
Plan participants’ contributions	2	2
Benefits paid, including lump sum and annuity transfers	(14)	(17)
Other, including foreign currency translation	0	0
Fair value of plan assets at end of year (estimated)	15	19	$ 18
Noncurrent assets	0	0
Current liabilities	(8)	(8)
Noncurrent liabilities	(126)	(124)
Funded status	(134)	$ (132)
Discount rate		3.00%
Other Post-employment Benefits | U.S.
Defined Benefit Plan Disclosure [Line Items]
Employer contributions and benefit payments	$ 6
Discount rate	2.10%	3.00%
Ultimate	4.50%	4.50%
Year when rate will reach Ultimate	2037	2037
Other Post-employment Benefits | Canada
Defined Benefit Plan Disclosure [Line Items]
Employer contributions and benefit payments	$ 2
Discount rate	2.40%	3.00%
Assumed for next year	5.30%	5.40%
Ultimate	4.00%	4.00%
Year when rate will reach Ultimate	2040	2039
Other Post-employment Benefits | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.10%
Assumed for next year	4.50%	4.50%
Ultimate	4.00%	4.00%
Other Post-employment Benefits | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%
Assumed for next year	6.80%	7.30%
Ultimate	4.50%	4.50%