EMPLOYEE BENEFIT PLANS - NET PENSION EXPENSE (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 65
Qualified Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 11	$ 12	32	$ 36
Interest cost	23	20	67	59
Expected return on assets	(24)	(27)	(71)	(80)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(1)	(1)	(1)	(1)
Recognized actuarial loss (gain)	9	9	27	25
Wages and Benefits [Member] | Qualified Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net pension expense	11	12	32	36
Nonoperating Income (Expense) [Member] | Qualified Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net pension expense	$ 7	$ 1	$ 22	$ 3