PENSION BENEFITS - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 1	$ 1
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	1,555	1,442	$ 1,604
Service cost	12	37	34
Interest cost	34	36	34
Expected return on plan assets	(56)	(54)	(47)
Curtailment loss	15	0	0
Amortization of actuarial losses	7	24	26
Net periodic benefit cost	$ 12	$ 43	$ 47