RISK MANAGEMENT ACTIVITIES - NOTIONAL VOLUMES (Details) - Non-hedge derivatives MMBTU in Thousands, kWh in Millions, bbl in Millions, T in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 kWh MMBTU T bbl	Dec. 31, 2014 kWh MMBTU T bbl
Natural gas contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh) | MMBTU	77,470	186,000
FTRs | Other transactions
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh) | kWh	8,577.9	4,287.7
Petroleum product contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (barrels) | bbl	0.1	0.1
Coal contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (tons)	2.2	3.0