RISK MANAGEMENT ACTIVITIES - NETTING ARRANGEMENTS (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets
Derivative assets subject to master netting or similar arrangements, gross amount	$ 7.7	$ 3.2
Potential effects of netting, including cash collateral	3.0	1.3
Derivative assets subject to master netting or similar arrangements, net amount	4.7	1.9
Derivative assets not subject to master netting or similar arrangements	0.0	1.3
Risk Management Assets	7.7	4.5
Total Risk Management Assets, Net Amount	4.7	3.2
Liabilities
Derivative liabilities subject to master netting or similar arrangements, gross amount	22.1	45.7
Potential effects of netting, including cash collateral	4.5	8.8
Derivative liabilities subject to master netting or similar arrangements, net amount	17.6	36.9
Derivative liabilities not subject to master netting or similar arrangement	7.4	3.4
Risk Management Liabilities	29.5	49.1
Total Risk Management Liabilities, Net Amount	$ 25.0	$ 40.3