REGULATORY ASSETS AND LIABILITIES (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Regulatory liabilities
Current	$ 67.5	$ 75.7
Long-term	332.5	316.2
Total	400.0	391.9
Removal costs
Regulatory liabilities
Total	298.0	278.1
Energy costs refundable through rate adjustments
Regulatory liabilities
Total	30.4	51.8
Unrecognized pension and other postretirement benefit costs
Regulatory liabilities
Total	18.4	20.0
Decoupling
Regulatory liabilities
Total	17.2	8.1
Uncollectible expense
Regulatory liabilities
Total	11.3	8.3
Derivatives
Regulatory liabilities
Total	9.3	6.0
Energy Efficiency Program
Regulatory liabilities
Total	5.4	7.2
Other:
Regulatory liabilities
Total	$ 10.0	$ 12.4