RISK MANAGEMENT ACTIVITIES - RISK MANAGEMENT ASSETS AND LIABILITIES (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	$ 242.4	$ 239.5
Long-term assets from risk management activities	98.5	75.4
Risk Management Assets	340.9	315.5
Current liabilities from risk management activities	165.7	163.8
Long-term liabilities from risk management activities	70.2	62.8
Risk Management Liabilities	235.9	226.6
Non-hedge derivatives
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	242.4	240.1
Long-term assets from risk management activities	98.5	75.4
Risk Management Assets	340.9	315.5
Current liabilities from risk management activities	165.7	163.8
Long-term liabilities from risk management activities	70.2	62.8
Risk Management Liabilities	235.9	226.6
Non-hedge derivatives | Utility segments | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	7.2	8.3
Long-term assets from risk management activities	0.7	1.8
Current liabilities from risk management activities	3.6	1.0
Long-term liabilities from risk management activities	0.7	0.1
Non-hedge derivatives | Utility segments | 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	0.3
Non-hedge derivatives | Utility segments | Petroleum product contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	0	0.1
Current liabilities from risk management activities	0.6	0
Non-hedge derivatives | Utility segments | 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	2.4	0.2
Current liabilities from risk management activities	2.3	1.9
Long-term liabilities from risk management activities	0.1	0.8
Non-hedge derivatives | Integrys Energy Services | Natural gas contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	61.1	57.6
Long-term assets from risk management activities	29.1	29.5
Current liabilities from risk management activities	46.2	42.9
Long-term liabilities from risk management activities	16.2	18.6
Non-hedge derivatives | Integrys Energy Services | Electric contracts
Derivative assets and liabilities from risk management activities
Current assets from risk management activities	170.7	172.0
Long-term assets from risk management activities	66.3	43.9
Current liabilities from risk management activities	112.6	117.7
Long-term liabilities from risk management activities	$ 53.2	$ 43.3