RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - ASSETS - ADDITIONAL INFORMATION (Details) - USD ($) $ in Millions	Jun. 30, 2017	Jun. 30, 2016
US Government Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	$ 2,494	$ 292
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	3,824	4,513
Corporate Bond Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	730	382
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	$ 2,547	$ 1,018