FAIR VALUE - LEVEL 3 RECONCILIATION (Details) (Utility segments, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	$ (6.9)	$ (1.3)
Net realized gains (losses) included in earnings	(1.2)	0.7
Net unrealized gains (losses) recorded as regulatory assets or liabilities	(4.5)	2.2
Purchases		(0.1)
Settlements	7.0	(0.7)
Balance at the end of the period	(5.6)	0.8
Impact on earnings of unrealized gains (losses) on level 3 instruments	0	0
Natural gas contracts
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	(6.6)
Net realized gains (losses) included in earnings	0
Net unrealized gains (losses) recorded as regulatory assets or liabilities	0
Settlements	6.6
Balance at the end of the period	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 the period	1.9	1.2
Net realized gains (losses) included in earnings	(1.2)	0.7
Net unrealized gains (losses) recorded as regulatory assets or liabilities	(0.2)	0
Purchases		(0.1)
Settlements	0.1	(1.3)
Balance at the end of the period	0.6	0.5
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 the period	(2.2)	(2.5)
Net realized gains (losses) included in earnings	0	0
Net unrealized gains (losses) recorded as regulatory assets or liabilities	(4.3)	2.2
Purchases		0
Settlements	0.3	0.6
Balance at the end of the period	$ (6.2)	$ 0.3