RISK MANAGEMENT ACTIVITIES - NETTING ARRANGEMENTS (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets
Derivative assets subject to master netting or similar arrangements, gross amount	$ 1.8	$ 3.2
Potential effects of netting, including cash collateral	1.2	1.3
Derivative assets subject to master netting or similar arrangements, net amount	0.6	1.9
Derivative assets not subject to master netting or similar arrangements	0	1.3
Risk Management Assets	1.8	4.5
Total Risk Management Assets, Net Amount	0.6	3.2
Liabilities
Derivative liabilities subject to master netting or similar arrangements, gross amount	35.9	45.7
Potential effects of netting, including cash collateral	5.5	8.8
Derivative liabilities subject to master netting or similar arrangements, net amount	30.4	36.9
Derivative liabilities not subject to master netting or similar arrangement	7.4	3.4
Risk Management Liabilities	43.3	49.1
Total Risk Management Liabilities, Net Amount	$ 37.8	$ 40.3