RISK MANAGEMENT ACTIVITIES (Details 4) (Utility Segments, 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		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	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 assets (long-term)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2013 Natural gas contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2012 Natural gas contracts Balance Sheet - Regulatory assets (long-term)	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 - Utility cost of fuel, natural gas and purchased power	Sep. 30, 2012 Natural gas contracts Income Statement - Utility cost of fuel, natural gas and purchased power	Sep. 30, 2013 Natural gas contracts Income Statement - Utility cost of fuel, natural gas and purchased power	Sep. 30, 2012 Natural gas contracts Income Statement - Utility cost of fuel, natural gas and purchased power	Sep. 30, 2013 Natural gas contracts Income Statement - Operating and maintenance expense	Sep. 30, 2012 Natural gas contracts Income Statement - Operating and maintenance expense	Sep. 30, 2013 Natural gas contracts Income Statement - Operating and maintenance expense	Sep. 30, 2012 Natural gas contracts Income Statement - Operating and maintenance expense	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 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 Contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory assets (current)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory assets (long-term)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory liabilities (current)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2013 Coal Contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2012 Coal Contracts Balance Sheet - Regulatory liabilities (long-term)	Sep. 30, 2013 Purchases Natural gas contracts Btu	Dec. 31, 2012 Purchases Natural gas contracts Btu	Sep. 30, 2013 Purchases Petroleum product contracts bbl	Dec. 31, 2012 Purchases Petroleum product contracts bbl	Sep. 30, 2013 Purchases Coal Contracts T	Dec. 31, 2012 Purchases Coal Contracts T	Sep. 30, 2013 Sales Natural gas contracts Btu	Dec. 31, 2012 Sales Natural gas contracts Btu	Sep. 30, 2013 Sales Petroleum product contracts bbl	Dec. 31, 2012 Sales Petroleum product contracts bbl	Sep. 30, 2013 Other transactions FTRs kWh	Dec. 31, 2012 Other transactions FTRs kWh
Risk management activities
Gains (losses) recorded related to non-hedge derivatives	$ (0.5)	$ 10.2	$ 6.9	$ 22.9	$ 1.8	$ 3.8	$ 1.6	$ 7.7	$ (0.4)	$ (3.4)	$ (0.2)	$ (2.9)	$ 0	$ 0.8	$ (0.3)	$ 1.3	$ 0	$ 0.1	$ 0	$ 0.2	$ (0.1)	$ 0.1	$ (0.2)	$ 0.1	$ 0.8	$ 0	$ 0	$ (0.4)	$ (0.2)	$ (0.2)	$ (0.3)	$ 0.5	$ 0.1	$ 0.2	$ 0	$ 0.1	$ 0	$ 0.1	$ 0	$ 0.1	$ (0.2)	$ 0.1	$ (0.2)	$ 0.1	$ (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 non-hedge derivative contracts (therms)																																																													1,104,100,000	1,072,600,000					1,700,000	100,000
Notional volume of outstanding non-hedge derivative contracts (kwh)																																																																							5,858,100,000	4,057,200,000
Notional volume of outstanding non-hedge derivative contracts (barrels)																																																															76,822.0	62,811.0					9,000.0	0.0
Notional volume of outstanding non-hedge derivative contracts (tons)																																																																	5,100,000	5,100,000