POSTRETIREMENT BENEFITS AND EMPLOYEE STOCK OWNERSHIP PLAN - AMOUNTS EXPECTED TO BE AMORTIZED FROM ACCUMULATED OTHER COMPREHENSIVE INCOME INTO NET PERIODIC BENEFIT COST (Details) - Subsequent Event $ in Millions	Jun. 30, 2021 USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	$ 401
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	25
Other Retiree Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	47
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	$ (59)