RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - ASSETS MEASURED AT FAIR VALUE ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Dec. 31, 2016	Jun. 30, 2016
Fair Value Asset	$ 7,433	$ 6,274
U.S. Government Securities
Fair Value Asset	5,599	4,839
Corporate Bond Securities
Fair Value Asset	1,804	1,407
Other Investments
Fair Value Asset	$ 30	$ 28