PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10		$ 8
Interest cost	35		43
Expected return on plan assets	(59)		(62)
Amortization of actuarial loss	30		30
Amortization of prior service cost (credit)	1		1
Settlement charge	0	$ (6)	455
Total net periodic benefit cost	17		475
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1		2
Amortization of actuarial loss	1		2
Amortization of prior service cost (credit)	0		(1)
Total net periodic benefit cost	$ 2		$ 3