FAIR VALUE (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Inputs Assets and Liabilities Quantitative Information
Risk Management Asset	$ 4.0	$ 3.9
Risk Management Liability	3.4	9.7
FTRs | Valuation Technique: Market-based | Average | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Forward market prices (in dollars per megawatt or ton)	116.47
Coal contract | Valuation Technique: Market-based | Minimum | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Forward market prices (in dollars per megawatt or ton)	12.21
Coal contract | Valuation Technique: Market-based | Maximum | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Forward market prices (in dollars per megawatt or ton)	14.63
Fair value measurements on a recurring basis | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Risk Management Asset	3.7	3.7
Risk Management Liability	3.1	9.1
Fair value measurements on a recurring basis | FTRs | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Risk Management Asset	2.2	1.2
Risk Management Liability	0.4	0.1
Fair value measurements on a recurring basis | Coal contract | Level 3
Fair Value Inputs Assets and Liabilities Quantitative Information
Risk Management Asset	1.5	2.5
Risk Management Liability	$ 2.7	$ 9.0