FAIR VALUE (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation
Balance at the beginning of period	$ (4.0)	$ (13.0)	$ (5.4)	$ (5.7)
Net realized gains included in earnings	0.4	1.9	1.0	2.0
Net unrealized (losses) gains recorded as regulatory assets or liabilities	2.7	5.1	5.6	(0.9)
Purchases	3.2	2.8	3.2	2.8
Sales	(0.1)	0	(0.1)	(0.1)
Settlements	(2.4)	(4.1)	(4.5)	(5.4)
Balance at the end of period	(0.2)	(7.3)	(0.2)	(7.3)
Unrealized Gain (Loss) Recognized in Income
Impact on earnings of unrealized gains and losses on Level 3 derivatives	0	0	0	0
FTRs
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation
Balance at the beginning of period	0.6	0.4	1.1	1.2
Net realized gains included in earnings	0.4	1.9	1.0	2.0
Net unrealized (losses) gains recorded as regulatory assets or liabilities	(0.9)	(0.1)	(1.1)	(0.3)
Purchases	3.2	2.8	3.2	2.8
Sales	(0.1)	0	(0.1)	(0.1)
Settlements	(1.1)	(2.5)	(2.0)	(3.1)
Balance at the end of period	2.1	2.5	2.1	2.5
Coal contract
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation
Balance at the beginning of period	(4.6)	(13.4)	(6.5)	(6.9)
Net realized gains included in earnings	0	0	0	0
Net unrealized (losses) gains recorded as regulatory assets or liabilities	3.6	5.2	6.7	(0.6)
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(1.3)	(1.6)	(2.5)	(2.3)
Balance at the end of period	$ (2.3)	$ (9.8)	$ (2.3)	$ (9.8)