RISK MANAGEMENT ACTIVITIES - NOTIONAL VOLUMES (Details) (Non-hedge derivatives)	3 Months Ended	12 Months Ended
	Mar. 31, 2014 Btu	Dec. 31, 2013 Btu
Natural gas contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (therms or kwh)	1,889,600,000	2,242,500,000
Natural gas contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (therms or kwh)	0	7,000,000
FTRs | Other Transactions
Risk management activities
Notional volume of outstanding derivative contracts (therms or kwh)	1,373,000,000	3,427,000,000
Petroleum product contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (barrels)	78,000.0	73,002.0
Petroleum product contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (barrels)	20,000.0	14,000.0
Coal contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (tons)	4,300,000	4,800,000
Coal contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (tons)	0	0