FAIR VALUE (Details 3) (USD $) In Millions, unless otherwise specified								6 Months Ended			6 Months Ended					6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Maximum	Jun. 30, 2013 Level 3 Fair value measurements on a recurring basis	Dec. 31, 2012 Level 3 Fair value measurements on a recurring basis	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis FTRs	Dec. 31, 2012 Utility Segments Level 3 Fair value measurements on a recurring basis FTRs	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis FTRs Weighted Average Market-based	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts	Dec. 31, 2012 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts Minimum Market-based	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts Maximum Market-based	Jun. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts	Dec. 31, 2012 Utility Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Minimum Monte Carlo Analysis Contingent consideration	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Maximum Monte Carlo Analysis Contingent consideration	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts	Dec. 31, 2012 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts Minimum Market-based	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts Maximum Market-based	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts	Dec. 31, 2012 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts Market-based	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts Minimum Market-based	Jun. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts Maximum Market-based
Significant internally-developed unobservable inputs
Risk Management Assets	$ 243.9	$ 190.7		$ 43.9	$ 19.6	$ 4.5	$ 2.1		$ 0	$ 2.5			$ 0	$ 0				$ 23.7	$ 5.4			$ 15.7	$ 9.6
Risk Management Liabilities	262.4	240.3		30.5	24.5	0.6	0.1		2.3	9.0			0	0				16.0	1.5			11.6	13.9
Forward market prices								164.99			11.90	14.50								(1.47)	6.13				(6.60)	10.86
Probability of default (as a percent)																				11.60%	51.00%			26.00%
Option volatilities (as a percent)																									19.80%	120.50%
Contingent Consideration			$ 8.0	$ 7.7											$ 7.7
Growth rate (as a percent)																(32.00%)	157.00%