RISK MANAGEMENT ACTIVITIES (Details 5) (Nonregulated Segments) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 USD ($)	Mar. 31, 2012 USD ($)	Mar. 31, 2013 Natural gas contracts Nonregulated revenue USD ($)	Mar. 31, 2012 Natural gas contracts Nonregulated revenue USD ($)	Mar. 31, 2013 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Mar. 31, 2012 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Mar. 31, 2013 Natural gas contracts Nonregulated cost of sales USD ($)	Mar. 31, 2013 Electric contracts Nonregulated revenue USD ($)	Mar. 31, 2012 Electric contracts Nonregulated revenue USD ($)	Mar. 31, 2013 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Mar. 31, 2012 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Mar. 31, 2013 Cash flow hedges Natural gas contracts USD ($)	Mar. 31, 2013 Cash flow hedges Electric contracts USD ($)	Mar. 31, 2013 Purchases Natural gas contracts therm	Dec. 31, 2012 Purchases Natural gas contracts therm	Mar. 31, 2013 Purchases Electric contracts kWh	Dec. 31, 2012 Purchases Electric contracts kWh	Mar. 31, 2013 Purchases Foreign exchange contracts CAD	Dec. 31, 2012 Purchases Foreign exchange contracts CAD	Mar. 31, 2013 Sales Natural gas contracts therm	Dec. 31, 2012 Sales Natural gas contracts therm	Mar. 31, 2013 Sales Electric contracts kWh	Dec. 31, 2012 Sales Electric contracts kWh	Mar. 31, 2013 Sales Foreign exchange contracts CAD	Dec. 31, 2012 Sales Foreign exchange contracts CAD
Risk management activities
Notional volume of outstanding non-hedge derivative contracts														641,500,000	782,000,000					556,200,000	679,000,000
Notional volume of outstanding non-hedge derivative contracts																56,100,100,000	54,127,600,000					34,502,000,000	31,809,600,000
Notional volume of outstanding foreign exchange non-hedge derivative contracts, monetary (in Canadian dollars)																		0.4	0.4					0.4	0.4
Gains (losses) recorded related to non-hedge derivatives					(0.1)	(1.2)				(1.0)	(0.7)
Gains (losses) recorded related to non-hedge derivatives			3.4	4.0			(1.6)	64.0	(68.6)
Gains (losses) recorded related to non-hedge derivatives	64.7	(66.5)
Pre-tax losses on cash flow hedge expected to be recognized in earnings in the next 12 months												$ (0.1)	$ (2.4)