RISK MANAGEMENT ACTIVITIES (Details 4) In Millions, unless otherwise specified	12 Months Ended																								1 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2011 Nonregulated Segments USD ($)	Dec. 31, 2010 Nonregulated Segments USD ($)	Dec. 31, 2009 Nonregulated Segments USD ($)	Dec. 31, 2010 Nonregulated Segments Interest expense. USD ($)	Dec. 31, 2009 Nonregulated Segments Interest expense. USD ($)	Dec. 31, 2011 Nonregulated Segments Natural gas contracts Nonregulated revenue USD ($)	Dec. 31, 2010 Nonregulated Segments Natural gas contracts Nonregulated revenue USD ($)	Dec. 31, 2011 Nonregulated Segments Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Dec. 31, 2010 Nonregulated Segments Natural gas contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Dec. 31, 2011 Nonregulated Segments Electric contracts Nonregulated revenue USD ($)	Dec. 31, 2010 Nonregulated Segments Electric contracts Nonregulated revenue USD ($)	Dec. 31, 2011 Nonregulated Segments Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Dec. 31, 2010 Nonregulated Segments Electric contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Dec. 31, 2009 Nonregulated Segments Foreign exchange contracts Nonregulated revenue USD ($)	Dec. 31, 2010 Nonregulated Segments Interest rate swaps Interest expense. USD ($)	Dec. 31, 2009 Nonregulated Segments Interest rate swaps Interest expense. USD ($)	Dec. 31, 2009 Nonregulated Segments Commodity contracts Nonregulated revenue USD ($)	Dec. 31, 2009 Nonregulated Segments Commodity contracts Nonregulated revenue (reclassified from accumulated OCI) USD ($)	Dec. 31, 2011 Nonregulated Segments Cash flow hedges USD ($)	Dec. 31, 2011 Nonregulated Segments Cash flow hedges Natural gas contracts USD ($)	Dec. 31, 2011 Nonregulated Segments Cash flow hedges Electric contracts USD ($)	Jan. 31, 2011 Nonregulated Segments Fair value hedges Interest rate swaps USD ($)	Dec. 31, 2011 Nonregulated Segments Purchases Natural gas contracts therm	Dec. 31, 2010 Nonregulated Segments Purchases Natural gas contracts therm	Dec. 31, 2011 Nonregulated Segments Purchases Electric contracts kWh	Dec. 31, 2010 Nonregulated Segments Purchases Electric contracts kWh	Dec. 31, 2011 Nonregulated Segments Purchases Foreign exchange contracts CAD	Dec. 31, 2010 Nonregulated Segments Purchases Foreign exchange contracts CAD	Dec. 31, 2011 Nonregulated Segments Sales Natural gas contracts therm	Dec. 31, 2010 Nonregulated Segments Sales Natural gas contracts therm	Dec. 31, 2011 Nonregulated Segments Sales Electric contracts kWh	Dec. 31, 2010 Nonregulated Segments Sales Electric contracts kWh	Dec. 31, 2011 Nonregulated Segments Sales Foreign exchange contracts CAD	Dec. 31, 2010 Nonregulated Segments Sales Foreign exchange contracts CAD
Risk management activities
Loss on cash flow hedge deferred in accumulated OCI																						$ 9.9
Pre-tax losses on cash flow hedge expected to be recognized in earnings in the next 12 months																							2.0	4.3
Unrealized gains (losses) recorded related to non-hedge derivatives											(2.3)	(1.6)			(1.7)	(3.7)					(3.2)
Unrealized gains (losses) recorded related to non-hedge derivatives									14.0	30.9			(79.0)	(92.7)			(1.8)	0.4	(1.7)	(5.1)
Unrealized gains (losses) recorded related to non-hedge derivatives				(69.0)	(66.7)	(11.8)
Notional volume of outstanding non-hedge derivative contracts																										959,200,000.0	940,600,000.0	34,405,700,000.0	22,149,400,000.0			797,100,000.0	1,048,400,000.0	20,374,000,000.0	19,707,000,000.0
Notional volume of outstanding foreign exchange non-hedge derivative contracts, monetary (in Canadian dollars)																														4.2	15.5					4.2	15.5
Value of hedged item																									50.0
Amount of debt repaid	565.8	117.2	157.8																						325.0
Interest rate stated percentage																									6.90%
Unrealized gain (loss) related to the fair value hedge																		(1.7)	(0.6)
Unrealized gain (loss) related to the debt hedged by swap							$ 1.7	$ 0.6