RISK MANAGEMENT ACTIVITIES (Details 7) (Nonregulated segments, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Risk management activities
Gains (losses) recorded related to non-hedge derivatives (total)	$ 89.8	$ (1.5)	$ (69.0)
Natural gas contracts | Nonregulated revenue
Risk management activities
Gains (losses) recorded related to non-hedge derivatives	36.7	6.8	14.0
Natural gas contracts | Nonregulated cost of sales
Risk management activities
Gains (losses) recorded related to non-hedge derivatives	(27.6)	0	0
Natural gas contracts | Nonregulated revenue (reclassified from Accumulated OCI)
Risk management activities
Gains (losses) recorded related to non-hedge derivatives (prior cash flow hedge)	(0.3)	(2.0)	(2.3)
Electric contracts | Nonregulated revenue
Risk management activities
Gains (losses) recorded related to non-hedge derivatives	73.6	(2.0)	(79.0)
Electric contracts | Nonregulated cost of sales
Risk management activities
Gains (losses) recorded related to non-hedge derivatives	10.8	0	0
Electric contracts | Nonregulated revenue (reclassified from Accumulated OCI)
Risk management activities
Gains (losses) recorded related to non-hedge derivatives (prior cash flow hedge)	$ (3.4)	$ (4.3)	$ (1.7)