FAIR VALUE - SIGNIFICANT UNOBSERVABLE INPUTS (Details) (USD $) In Millions, unless otherwise specified							9 Months Ended			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Fair value measurements on a recurring basis Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis Level 3	Sep. 30, 2014 Fair value measurements on a recurring basis FTRs Level 3	Dec. 31, 2013 Fair value measurements on a recurring basis FTRs Level 3	Sep. 30, 2014 Fair value measurements on a recurring basis FTRs Level 3 Valuation Technique: Market-based Average	Sep. 30, 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	Sep. 30, 2014 Fair value measurements on a recurring basis Coal contracts Level 3 Valuation Technique: Market-based Minimum	Sep. 30, 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	$ 7.2	$ 2.4	$ 5.8	$ 1.7	$ 3.4	$ 1.5		$ 2.4	$ 0.2
Risk Management Liability	$ 3.5	$ 3.1	$ 2.8	$ 3.0	$ 0.4	$ 0.3		$ 2.4	$ 2.7
Fair Value Inputs
Forward market prices (in dollars per megawatt-month or ton)							187.89			12.31	15.50