POSTRETIREMENT BENEFITS AND EMPLOYEE STOCK OWNERSHIP PLAN - RECONCILIATION OF BENEFIT PLANS RECOGNIZED IN THE BALANCE SHEET (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018
Pension Plan
CLASSIFICATION OF NET AMOUNT RECOGNIZED
Assets for Plan Benefits, Defined Benefit Plan	$ 19	$ 420
Liability, Defined Benefit Plan, Current	(52)	(43)
Liability, Defined Benefit Plan, Noncurrent	(5,622)	(4,768)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(5,655)	(4,391)
AMOUNTS RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (AOCI)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	5,062	3,787
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax	214	244
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	5,276	4,031
Other Retiree Benefits
CLASSIFICATION OF NET AMOUNT RECOGNIZED
Assets for Plan Benefits, Defined Benefit Plan	1,257	0
Liability, Defined Benefit Plan, Current	(27)	(24)
Liability, Defined Benefit Plan, Noncurrent	(1,098)	(1,495)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	132	(1,519)
AMOUNTS RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (AOCI)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	874	2,366
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax	(424)	(478)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	$ 450	$ 1,888