RISK MANAGEMENT ACTIVITIES (Details 5) (Nonregulated Segments) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated revenue USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated revenue USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated revenue USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated revenue USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated cost of sales USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated cost of sales USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated cost of sales USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated cost of sales USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2013 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2012 Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2013 Electric contracts Nonregulated revenue USD ($)	Sep. 30, 2012 Electric contracts Nonregulated revenue USD ($)	Sep. 30, 2013 Electric contracts Nonregulated revenue USD ($)	Sep. 30, 2012 Electric contracts Nonregulated revenue USD ($)	Sep. 30, 2013 Electric contracts Nonregulated cost of sales USD ($)	Sep. 30, 2012 Electric contracts Nonregulated cost of sales USD ($)	Sep. 30, 2013 Electric contracts Nonregulated cost of sales USD ($)	Sep. 30, 2012 Electric contracts Nonregulated cost of sales USD ($)	Sep. 30, 2013 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2012 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2013 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2012 Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Sep. 30, 2013 Purchases Natural gas contracts Btu	Dec. 31, 2012 Purchases Natural gas contracts Btu	Sep. 30, 2013 Purchases Electric contracts kWh	Dec. 31, 2012 Purchases Electric contracts kWh	Sep. 30, 2013 Purchases Foreign exchange contracts CAD	Dec. 31, 2012 Purchases Foreign exchange contracts CAD	Sep. 30, 2013 Sales Natural gas contracts Btu	Dec. 31, 2012 Sales Natural gas contracts Btu	Sep. 30, 2013 Sales Electric contracts kWh	Dec. 31, 2012 Sales Electric contracts kWh	Sep. 30, 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 (therms)																													1,108,500,000	782,000,000					1,011,800,000	679,000,000
Notional volume of outstanding non-hedge derivative contracts (kwh)																															50,956,900,000	54,127,600,000					32,059,600,000	31,809,600,000
Notional volume of outstanding foreign exchange non-hedge derivative contracts, monetary (in Canadian dollars)																																	0	0.4					0	0.4
Gains (losses) recorded related to non-hedge derivatives					(21.1)	(4.4)	16.1	7.0	25.0	0	(9.5)	0					36.0	49.1	22.4	(10.5)	(6.6)	0	2.1	0
Gains (losses) recorded related to non-hedge derivatives (prior cash flow hedge)													0	(0.1)	(0.2)	(1.6)									(0.2)	(1.9)	(3.2)	(3.3)
Gains (losses) recorded related to non-hedge derivatives (total)	$ 33.1	$ 42.7	$ 27.7	$ (8.4)