POSTRETIREMENT BENEFITS AND EMPLOYEE STOCK OWNERSHIP PLAN - RECONCILIATION OF BENEFIT PLANS RECOGNIZED IN THE BALANCE SHEET (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019
Pension Plan
CLASSIFICATION OF NET AMOUNT RECOGNIZED
Assets for Plan Benefits, Defined Benefit Plan	$ 12	$ 19
Liability, Defined Benefit Plan, Current	(66)	(52)
Liability, Defined Benefit Plan, Noncurrent	(6,223)	(5,622)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(6,277)	(5,655)
AMOUNTS RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (AOCI)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	5,662	5,062
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax	198	214
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	5,860	5,276
Other Retiree Benefits
CLASSIFICATION OF NET AMOUNT RECOGNIZED
Assets for Plan Benefits, Defined Benefit Plan	1,843	1,257
Liability, Defined Benefit Plan, Current	(30)	(27)
Liability, Defined Benefit Plan, Noncurrent	(965)	(1,098)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	848	132
AMOUNTS RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (AOCI)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	572	874
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax	(511)	(424)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	$ 61	$ 450