RISK MANAGEMENT ACTIVITIES - NOTIONAL VOLUMES (Details) (Non-hedge derivatives)	12 Months Ended
	Dec. 31, 2014 MMBTU	Dec. 31, 2013 MMBTU
Natural gas contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	102,540,000	224,250,000
Natural gas contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)		700,000
FTRs | Other Transactions
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	4,287,700,000	3,427,000,000
Petroleum product contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (barrels)	0	100,000
Petroleum product contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (barrels)		0
Coal contract | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (tons)	3,000,000	4,800,000
Coal contract | Sales
Risk management activities
Notional volume of outstanding derivative contracts (tons)		0