RISK MANAGEMENT ACTIVITIES - UTILITY SEGMENTS, NOTIONAL VOLUMES (Details) (Non-hedge derivatives, Utility segments)	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)	2,438,800,000	3,124,800,000
Natural gas contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (therms or kwh)	2,100,000	29,300,000
FTRs | Other transactions
Risk management activities
Notional volume of outstanding derivative contracts (therms or kwh)	1,448,700,000	3,633,100,000
Petroleum product contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (barrels)	113,000.0	102,811.0
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 non-hedge derivative contracts (tons)	4,300,000	4,800,000
Coal contracts | Sales
Risk management activities
Notional volume of outstanding non-hedge derivative contracts (tons)	0	0