RISK MANAGEMENT ACTIVITIES - RISK MANAGEMENT ASSETS AND LIABILITIES (Details) (Utility segments, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivative assets and liabilities from risk management activities
Risk Management Assets	$ 4.5	$ 11.9
Risk Management Liabilities	49.1	4.1
Non-hedge derivatives
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	4.0	9.9
Long-term assets from risk management activities	0.5	2.0
Risk Management Assets	4.5	11.9
Current liabilities from risk management activities	42.7	3.2
Long-term liabilities from risk management activities	6.4	0.9
Risk Management Liabilities	49.1	4.1
Non-hedge derivatives | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	1.8	8.3
Long-term assets from risk management activities	0.5	1.8
Current liabilities from risk management activities	37.3	1.0
Long-term liabilities from risk management activities	5.3	0.1
Non-hedge derivatives | FTRs
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	2.2	1.5
Current liabilities from risk management activities	0.3	0.3
Non-hedge derivatives | Petroleum product contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0	0.1
Long-term assets from risk management activities	0
Current liabilities from risk management activities	2.7	0
Long-term liabilities from risk management activities	0.1
Non-hedge derivatives | Coal contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0	0
Long-term assets from risk management activities	0	0.2
Current liabilities from risk management activities	2.4	1.9
Long-term liabilities from risk management activities	$ 1.0	$ 0.8