FAIR VALUE MEASUREMENTS 3 (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2015 |
Jun. 30, 2014 |
Jun. 30, 2015 |
Jun. 30, 2014 |
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||||
| Balance at beginning of period | $ 102 | $ 95 | $ 107 | $ 99 |
| Realized and unrealized gains (losses) | (60) | 5 | (54) | 6 |
| Allocated transmission instruments | 1 | 0 | 1 | 1 |
| Settlements | (1) | (15) | (12) | (21) |
| Balance at end of period | 42 | 85 | 42 | 85 |
| Change in unrealized gains (losses) relating to instruments still held at period end | 45 | 0 | 46 | 0 |
| CRR Auction Rate Per MWh, Minimum | (16) | (6) | (16) | (6) |
| CRR Auction Rate Per MWh, Maximum | $ 8 | $ 12 | $ 8 | $ 12 |