FAIR VALUE - LEVEL 3 RECONCILIATION (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of period	$ 0.8	$ (4.0)	$ (1.3)	$ (5.4)
Net realized gains included in earnings	0.1	0.4	0.8	1.0
Net unrealized gains (losses) recorded as regulatory assets or liabilities	0.9	2.7	3.1	5.6
Purchases	4.4	3.2	4.3	3.2
Sales		(0.1)		(0.1)
Settlements	(1.3)	(2.4)	(2.0)	(4.5)
Balance at the end of the period	4.9	(0.2)	4.9	(0.2)
Impact on earnings of unrealized gains (losses) on level 3 instruments	0	0	0	0
FTRs
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of period	0.5	0.6	1.2	1.1
Net realized gains included in earnings	0.1	0.4	0.8	1.0
Net unrealized gains (losses) recorded as regulatory assets or liabilities	0.1	(0.9)	0.1	(1.1)
Purchases	4.4	3.2	4.3	3.2
Sales		(0.1)		(0.1)
Settlements	(1.1)	(1.1)	(2.4)	(2.0)
Balance at the end of the period	4.0	2.1	4.0	2.1
Coal contracts
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of period	0.3	(4.6)	(2.5)	(6.5)
Net realized gains included in earnings	0	0	0	0
Net unrealized gains (losses) recorded as regulatory assets or liabilities	0.8	3.6	3.0	6.7
Purchases	0	0	0	0
Sales		0		0
Settlements	(0.2)	(1.3)	0.4	(2.5)
Balance at the end of the period	$ 0.9	$ (2.3)	$ 0.9	$ (2.3)