RETIREMENT AND POSTRETIREMENT BENEFIT PLANS - Summary of Net Benefit Costs (Details) - Direct Plan - Pension Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1	$ 1	$ 3	$ 3
Expected return on plan assets	(3)	(2)	(7)	(6)
Actuarial loss (gain)	0	0	1	1
Net periodic pension expense (benefit)	$ (2)	$ (1)	$ (3)	$ (2)