FAIR VALUE MEASUREMENTS - RECON OF LEVEL 3 ASSETS (Details) - USD ($) |
3 Months Ended | |||
|---|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||||
| Balance at beginning of period | $ 19,000,000 | $ 107,000,000 | ||
| Realized and unrealized gains (losses) | (1,000,000) | 6,000,000 | ||
| Settlements | (7,000,000) | (11,000,000) | ||
| Balance at end of period | 11,000,000 | 102,000,000 | ||
| Change in unrealized gains relating to instruments still held at the end of the period | (1,000,000) | $ 1,000,000 | ||
| Maximum [Member] | ||||
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||||
| Congestion Revenue Rights | $ 10 | $ 8 | ||
| Market Electricity Forward Price Inputs | 57.43 | |||
| Minimum [Member] | ||||
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||||
| Congestion Revenue Rights | $ (24) | $ (16) | ||
| Market Electricity Forward Price Inputs | $ 15.85 | |||