RISK MANAGEMENT ACTIVITIES (Details 2) (USD $) 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		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 Natural gas contracts Derivative Purchases Btu	Dec. 31, 2012 Natural gas contracts Derivative Purchases Btu	Sep. 30, 2013 Natural gas contracts Derivative Sales Btu	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2013 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Sep. 30, 2012 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Sep. 30, 2013 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Sep. 30, 2012 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Sep. 30, 2013 FTRs Derivative Other Transactions kWh	Dec. 31, 2012 FTRs Derivative Other Transactions kWh	Sep. 30, 2013 FTRs Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 FTRs Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 FTRs Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 FTRs Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Petroleum product contracts Derivative Purchases bbl	Dec. 31, 2012 Petroleum product contracts Derivative Purchases bbl	Sep. 30, 2013 Petroleum product contracts Derivative Sales bbl	Sep. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Petroleum product contracts Income Statement - Operating and maintenance expense	Sep. 30, 2012 Petroleum product contracts Income Statement - Operating and maintenance expense	Sep. 30, 2013 Petroleum product contracts Income Statement - Operating and maintenance expense	Sep. 30, 2012 Petroleum product contracts Income Statement - Operating and maintenance expense	Sep. 30, 2013 Coal contract Derivative Purchases T	Dec. 31, 2012 Coal contract Derivative Purchases T	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory assets (long Term)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory assets (long Term)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2013 Coal contract Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Coal contract Balance Sheet - Regulatory liabilities (long-term)
Derivative [Line Items]
Unrealized gains (losses)				$ (0.2)	$ 0.3	$ 0.3	$ 2.8	$ 0	$ 0.3	$ (0.1)	$ 0.6	$ 0	$ 0.1	$ 0	$ 0.1	$ 0	$ 0.1	$ 0	$ 0.2			$ 0.8	$ 0	$ 0	$ (0.6)	$ 0	$ 0	$ (0.3)	$ 0.3				$ 0.1	$ 0.2	$ 0	$ 0.1	$ 0	$ 0.1	$ 0	$ 0.1	$ (0.1)	$ 0	$ (0.1)	$ 0			$ (0.6)	$ 0.7	$ 2.1	$ (2.5)	$ 0.2	$ (0.1)	$ 4.2	$ 0.1	$ 0	$ 0	$ (0.3)	$ 0	$ 1.5	$ 0	$ (0.7)	$ 0
Notional volume of outstanding derivative contracts (therms)	200,200,000	86,100,000	0
Notional volume of outstanding derivative contracts (kwh)																				5,524,800,000	3,838,200,000
Notional volume of outstanding derivative contracts (barrels)																														36,803.0	33,002.0	9,000.0
Notional volume of outstanding derivative contracts (tons)																																													5,100,000	5,100,000