RISK MANAGEMENT ACTIVITIES (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	$ 182.5	$ 145.4
Long-term Assets from Risk Management Activities	50.3	45.3
Current Liabilities from Risk Management Activities	140.9	181.9
Long-term Liabilities from Risk Management Activities	49.3	58.4
Risk Management Assets	232.8	190.7
Risk Management Liabilities	190.2	240.3
Utility Segments | Cash flow hedges | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current Liabilities from Risk Management Activities	0.1	0.4
Utility Segments | Nonhedge derivatives | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	9.8	2.5
Long-term Assets from Risk Management Activities	1.9	0.9
Current Liabilities from Risk Management Activities	3.7	14.0
Long-term Liabilities from Risk Management Activities		0.8
Utility Segments | Nonhedge derivatives | FTRs
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	1.0	2.1
Current Liabilities from Risk Management Activities	0.1	0.1
Utility Segments | Nonhedge derivatives | Petroleum product contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0.1	0.2
Utility Segments | Nonhedge derivatives | Coal contract
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0.1	0.3
Long-term Assets from Risk Management Activities		2.2
Current Liabilities from Risk Management Activities	2.8	4.7
Long-term Liabilities from Risk Management Activities	2.0	4.3
Nonregulated Segments | Nonhedge derivatives | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	24.3	51.7
Long-term Assets from Risk Management Activities	10.0	11.5
Current Liabilities from Risk Management Activities	19.7	48.5
Long-term Liabilities from Risk Management Activities	5.3	7.6
Nonregulated Segments | Nonhedge derivatives | Electric contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	147.2	88.6
Long-term Assets from Risk Management Activities	38.4	30.7
Current Liabilities from Risk Management Activities Including Amounts Classified As Held For Sale	114.5	114.2
Long-term Liabilities from Risk Management Activities	$ 42.0	$ 45.7