FAIR VALUE (Details 3) (USD $) In Millions, unless otherwise specified							9 Months Ended			9 Months Ended					9 Months Ended			9 Months Ended			9 Months Ended				9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Level 3 Fair value measurements on a recurring basis	Dec. 31, 2012 Level 3 Fair value measurements on a recurring basis	Sep. 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	Sep. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis FTRs Weighted Average Market-based	Sep. 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	Sep. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts Minimum Market-based	Sep. 30, 2013 Utility Segments Level 3 Fair value measurements on a recurring basis Coal contracts Maximum Market-based	Sep. 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	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Contingent consideration	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Market-based	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Minimum Monte Carlo Analysis Contingent consideration	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Maximum Contingent consideration	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Maximum Monte Carlo Analysis Contingent consideration	Sep. 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	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts Minimum Market-based	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Natural gas contracts Maximum Market-based	Sep. 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	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts Market-based	Sep. 30, 2013 Nonregulated Segments Level 3 Fair value measurements on a recurring basis Electric contracts Minimum Market-based	Sep. 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	$ 213.0	$ 190.7	$ 39.0	$ 19.6	$ 3.4	$ 2.1		$ 1.5	$ 2.5			$ 0	$ 0						$ 21.3	$ 5.4			$ 12.8	$ 9.6
Risk Management Liabilities	217.1	240.3	22.9	24.5	0.4	0.1		2.7	9.0			0	0						9.7	1.5			10.1	13.9
Contingent Consideration														$ 7.7			$ 8.0
Growth rate (as a percent)																(32.00%)		157.00%
Forward market prices							180.59			12.21	14.63										(2.36)	8.17				(7.15)	9.25
Probability of default (as a percent)																					11.60%	51.00%			26.00%
Counterparty default time period															1 year
Option volatilities (as a percent)																										19.30%	118.00%
Monthly curve shaping (as a percent)																										(37.50%)	25.60%