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
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Natural gas contracts Purchases therm	Dec. 31, 2011 Natural gas contracts Purchases therm	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Natural gas contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 Natural gas contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2011 Natural gas contracts Income Statement - Cost of fuel, natural gas and purchased power	Jun. 30, 2012 FTRs Other transactions kwh	Dec. 31, 2011 FTRs Other transactions kwh	Jun. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 FTRs Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 FTRs Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2012 Petroleum product contracts Purchases bbl	Dec. 31, 2011 Petroleum product contracts Purchases bbl	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Petroleum product contracts Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 Petroleum product contracts Balance Sheet - Regulatory liabilities (current)	Jun. 30, 2011 Petroleum product contracts Income Statement - Operating and maintenance expense	Jun. 30, 2011 Petroleum product contracts Income Statement - Operating and maintenance expense	Jun. 30, 2012 Coal contract Purchases T	Dec. 31, 2011 Coal contract Purchases T	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2011 Coal contract Balance Sheet - Regulatory assets (current)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2011 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2012 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2011 Coal contract Balance Sheet - Regulatory assets (long Term)	Jun. 30, 2011 Coal contract Balance Sheet - Regulatory liabilities (long-term)
Risk management activities
Unrealized gains (losses)					$ 0.8	$ (0.1)	$ 2.5	$ 2.4	$ 0.3	$ 0.3	$ (0.1)	$ 0.1	$ 0.1			$ (0.8)	$ (0.8)	$ (0.6)	$ (0.7)	$ 0.7	$ 1.2	$ 0.3	$ 0.1			$ (0.2)	$ (0.1)	$ (0.1)	$ (0.1)	$ (0.1)	$ (0.2)	$ 0.2	$ (0.1)	$ 0.1			$ (0.1)	$ 0.3	$ (3.2)	$ (0.2)	$ 3.7	$ 0.2	$ 0.2	$ (3.0)	$ (3.7)
Notional volume of outstanding derivative contracts			72,200,000.0	58,400,000.0										8,480,000,000.0	4,814,800,000.0									29,324.0	26,770.0										3,700,000.0	4,100,000.0
Cash collateral provided to others	$ 4.6	$ 4.1