FAIR VALUE MEASUREMENTS 3 (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 42	$ 85	$ 107	$ 99
Realized and unrealized gains (losses)	(49)	3	(103)	9
Allocated transmission instruments	0	9	1	10
Settlements	43	(10)	31	(31)
Balance at end of period	36	87	36	87
Change in unrealized gains (losses) relating to instruments still held at period end	(8)	0	(54)	0
CRR Auction Rate Per MWh, Minimum	(16)	(6)	(16)	(6)
CRR Auction Rate Per MWh, Maximum	$ 8	$ 12	$ 8	$ 12