RISK MANAGEMENT ACTIVITIES (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	$ 154.9	$ 145.4
Long-term assets from risk management activities	58.1	45.3
Risk Management Assets	213.0	190.7
Current liabilities from risk management activities	157.5	181.9
Long-term liabilities from risk management activities	59.6	58.4
Risk Management Liabilities	217.1	240.3
Utility Segments | Non-hedge derivatives | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	2.2	2.5
Long-term assets from risk management activities	0.5	0.9
Current liabilities from risk management activities	5.4	14.0
Long-term liabilities from risk management activities	0.6	0.8
Utility Segments | Non-hedge derivatives | FTRs
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	3.4	2.1
Current liabilities from risk management activities	0.4	0.1
Utility Segments | Non-hedge derivatives | Petroleum product contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0	0.2
Current liabilities from risk management activities	0.2	0
Utility Segments | Non-hedge derivatives | Coal Contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0	0.3
Long-term assets from risk management activities	1.5	2.2
Current liabilities from risk management activities	2.6	4.7
Long-term liabilities from risk management activities	0.1	4.3
Utility Segments | Cash flow hedges | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities		0
Current liabilities from risk management activities		0.4
Nonregulated Segments | Non-hedge derivatives | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	48.9	51.7
Long-term assets from risk management activities	24.6	11.5
Current liabilities from risk management activities	37.6	48.5
Long-term liabilities from risk management activities	14.6	7.6
Nonregulated Segments | Non-hedge derivatives | Electric contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	100.4	88.6
Long-term assets from risk management activities	31.5	30.7
Current liabilities from risk management activities	111.3	114.2
Long-term liabilities from risk management activities	$ 44.3	$ 45.7