REGULATORY ASSETS AND LIABILITIES (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory liabilities
Current liabilities	$ 101.5	$ 65.6
Long-term liabilties	400.9	370.5
Total regulatory liabilities	502.4	436.1
Removal costs
Regulatory liabilities
Total regulatory liabilities	335.3	318.4
Decoupling
Regulatory liabilities
Total regulatory liabilities	51.7	15.9
Unrecognized pension and other postretirement benefit costs
Regulatory liabilities
Total regulatory liabilities	30.2	17.7
Energy costs refundable through rate adjustments
Regulatory liabilities
Total regulatory liabilities	27.2	44.4
Energy efficiency programs
Regulatory liabilities
Total regulatory liabilities	19.6	8.8
Uncollectible expense
Regulatory liabilities
Total regulatory liabilities	10.1	10.0
Crane Creek depreciation deferral
Regulatory liabilities
Total regulatory liabilities	9.0	9.4
Derivatives
Regulatory liabilities
Total regulatory liabilities	6.6	4.3
Fox Energy Center
Regulatory liabilities
Total regulatory liabilities	5.6	0
Other disclosures
Amount of allowance for earnings on equity capitalized for rate making purposes	26.7
Other
Regulatory liabilities
Total regulatory liabilities	$ 7.1	$ 7.2