FAIR VALUE - SIGNIFICANT UNOBSERVABLE INPUTS (Details) (USD $) In Millions, unless otherwise specified							3 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Fair value measurements on a recurring basis Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis Level 3	Mar. 31, 2014 Fair value measurements on a recurring basis FTRs Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis FTRs Level 3	Mar. 31, 2014 Fair value measurements on a recurring basis FTRs Level 3 Valuation Technique: Market-based Average	Mar. 31, 2014 Fair value measurements on a recurring basis Coal contracts Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis Coal contracts Level 3	Mar. 31, 2014 Fair value measurements on a recurring basis Coal contracts Level 3 Valuation Technique: Market-based Minimum	Mar. 31, 2014 Fair value measurements on a recurring basis Coal contracts Level 3 Valuation Technique: Market-based Maximum
Fair Value Inputs Assets and Liabilities Quantitative Information
Risk Management Asset	$ 3.2	$ 2.4	$ 2.5	$ 1.7	$ 0.7	$ 1.5		$ 1.8	$ 0.2
Risk Management Liability	$ 1.8	$ 3.1	$ 1.7	$ 3.0	$ 0.2	$ 0.3		$ 1.5	$ 2.7
Fair Value Inputs
Forward market prices (in dollars per megawatt-month or ton)							131.16			12.11	15.25