RISK MANAGEMENT ACTIVITIES (Details 2) (USD $) In Millions, unless otherwise specified				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013 Natural gas contracts Derivative Purchases [Member] Btu	Dec. 31, 2012 Natural gas contracts Derivative Purchases [Member] Btu	Jun. 30, 2013 Natural gas contracts Derivative Sales [Member] Btu	Jun. 30, 2013 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2012 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2013 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2012 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2013 FTRs Derivative Other Transactions [Member] kWh	Dec. 31, 2012 FTRs Derivative Other Transactions [Member] kWh	Jun. 30, 2013 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Petroleum product contracts Derivative Purchases [Member] bbl	Dec. 31, 2012 Petroleum product contracts Derivative Purchases [Member] bbl	Jun. 30, 2013 Petroleum product contracts Derivative Sales [Member] bbl	Jun. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Coal contract Derivative Purchases [Member] T	Dec. 31, 2012 Coal contract Derivative Purchases [Member] T	Jun. 30, 2013 Coal contract Derivative Sales [Member] T	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Jun. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (long-term)
Derivative [Line Items]
Unrealized gains (losses)				$ (0.5)	$ 0.8	$ 0.5	$ 2.5	$ (0.9)	$ 0.3	$ (0.1)	$ 0.3	$ 0	$ 0	$ 0	$ 0.1			$ (1.0)	$ (0.8)	$ (0.8)	$ (0.6)	$ 0.1	$ 0.7	$ (0.3)	$ 0.3				$ (0.1)	$ (0.2)	$ (0.1)	$ (0.1)	$ 0	$ (0.1)	$ 0	$ 0				$ 0.8	$ (0.1)	$ 2.7	$ (3.2)	$ 1.7	$ 3.7	$ 4.0	$ 0.2	$ (0.1)	$ 0	$ (0.3)	$ 0	$ 0	$ 0	$ (2.2)	$ 0
Notional volume of outstanding derivative contracts	65,500,000	86,100,000	0
Notional volume of outstanding derivative contracts																7,884,100,000	3,838,200,000
Notional volume of outstanding derivative contracts																										36,370.0	33,002.0	9,000.0
Notional volume of outstanding derivative contracts																																					4,400,000	5,100,000	100,000