POSTRETIREMENT BENEFITS AND EMPLOYEE STOCK OWNERSHIP PLAN - ADDITIONAL INFORMATION (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 1991	Jun. 30, 1989
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation			$ 14,512	$ 15,546
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets Range Minimum			8.00%
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets Range Maximum			9.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	[1]		6.90%	7.20%	7.20%
Pension Plan | Series A Preferred Stock
Defined Benefit Plan Disclosure [Line Items]
Employee Stock Ownership Plan (ESOP), Debt Structure, Direct Loan, Amount							$ 1,000
Employee Stock Ownership Plan (ESOP), Debt Structure, Employer Loan Guarantee			$ 62
Preferred Stock, Dividends, Per Share, Cash Paid			$ 2.70
Preferred Stock, Liquidation Preference Per Share			$ 6.82
Other Retiree Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	[1]		8.30%	8.30%	8.30%
Other Retiree Benefits | Series B Preferred Stock
Defined Benefit Plan Disclosure [Line Items]
Employee Stock Ownership Plan (ESOP), Debt Structure, Direct Loan, Amount						$ 1,000
Employee Stock Ownership Plan (ESOP), Debt Structure, Employer Loan Guarantee			$ 770
Preferred Stock, Dividends, Per Share, Cash Paid			$ 2.70
Preferred Stock, Liquidation Preference Per Share			$ 12.96
Treasury Stock
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets			8.50%
Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets Range Minimum			5.00%
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets Range Maximum			6.00%
Subsequent Event | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 125
Subsequent Event | Other Retiree Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		39
Contribution to Unfunded Plans | Subsequent Event | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		75
Contribution to Unfunded Plans | Subsequent Event | Other Retiree Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		24
Contribution to Funded Plans | Subsequent Event | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		50
Contribution to Funded Plans | Subsequent Event | Other Retiree Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 15

[1] Determined as of beginning of year.