RISK MANAGEMENT ACTIVITIES - RISK MANAGEMENT ASSETS AND LIABILITIES (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative assets and liabilities from risk management activities
Assets from risk management activities	$ 269.9	$ 239.5
Assets from risk management activities	60.3	75.4
Risk Management Assets	330.4	315.5
Liabilities from risk management activities	175.8	163.8
Liabilities from risk management activities	46.2	62.8
Risk Management Liabilities	222.0	226.6
Non-hedge derivatives
Derivative assets and liabilities from risk management activities
Assets from risk management activities	270.1	240.1
Assets from risk management activities	60.3	75.4
Risk Management Assets	330.4	315.5
Liabilities from risk management activities	175.8	163.8
Liabilities from risk management activities	46.2	62.8
Risk Management Liabilities	222.0	226.6
Non-hedge derivatives | Utility segments | Natural gas contracts
Derivative assets and liabilities from risk management activities
Assets from risk management activities	12.3	8.3
Assets from risk management activities	1.0	1.8
Liabilities from risk management activities	0.3	1.0
Liabilities from risk management activities	0.1	0.1
Non-hedge derivatives | Utility segments | FTRs
Derivative assets and liabilities from risk management activities
Assets from risk management activities	0.9	2.1
Liabilities from risk management activities	0.2	0.3
Non-hedge derivatives | Utility segments | FTRs | UPPCO
Disclosures related to the disposal
Current risk management assets classified as held for sale	0.2	0.6
Non-hedge derivatives | Utility segments | Petroleum product contracts
Derivative assets and liabilities from risk management activities
Assets from risk management activities	0.1	0.1
Liabilities from risk management activities	0	0
Non-hedge derivatives | Utility segments | Coal contracts
Derivative assets and liabilities from risk management activities
Assets from risk management activities	0	0
Assets from risk management activities	1.8	0.2
Liabilities from risk management activities	1.1	1.9
Liabilities from risk management activities	0.4	0.8
Non-hedge derivatives | Nonregulated segments | Natural gas contracts
Derivative assets and liabilities from risk management activities
Assets from risk management activities	56.0	57.6
Assets from risk management activities	20.9	29.5
Liabilities from risk management activities	41.7	42.9
Liabilities from risk management activities	10.9	18.6
Non-hedge derivatives | Nonregulated segments | Electric contracts
Derivative assets and liabilities from risk management activities
Assets from risk management activities	200.8	172.0
Assets from risk management activities	36.6	43.9
Liabilities from risk management activities	132.5	117.7
Liabilities from risk management activities	$ 34.8	$ 43.3