RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - ASSETS - ADDITIONAL INFORMATION (Details) - USD ($) $ in Millions |
Jun. 30, 2016 |
Jun. 30, 2015 |
|---|---|---|
| US Government Debt Securities | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis | $ 292 | $ 700 |
| Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis | 4,513 | 2,789 |
| Corporate Bond Securities | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis | 382 | 221 |
| Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis | $ 1,018 | $ 1,052 |