SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2012 town segment
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Number of business segments	3
Number of towns to which water service is provided	3
Gas
Operating revenues
% of revenue (as a percent)	7.10%
Number of customers	44,000
Gas | Residential
Operating revenues
% of revenue (as a percent)	62.10%
Gas | Commercial
Operating revenues
% of revenue (as a percent)	27.10%
Gas | Industrial
Operating revenues
% of revenue (as a percent)	1.20%
Gas | Other electric revenues
Operating revenues
% of revenue (as a percent)	9.60%
Electric
Operating revenues
% of revenue (as a percent)	91.70%
Number of customers	167,900
Electric | Water
Operating revenues
% of revenue (as a percent)	0.30%
Electric | Missouri
Operating revenues
% of revenue (as a percent)	89.30%
Electric | Kansas
Operating revenues
% of revenue (as a percent)	5.10%
Electric | Arkansas
Operating revenues
% of revenue (as a percent)	2.70%
Electric | Oklahoma
Operating revenues
% of revenue (as a percent)	2.90%
Electric | Residential
Operating revenues
% of revenue (as a percent)	42.20%
Electric | Commercial
Operating revenues
% of revenue (as a percent)	31.20%
Electric | Industrial
Operating revenues
% of revenue (as a percent)	15.50%
Electric | Wholesale on-system
Operating revenues
% of revenue (as a percent)	3.60%
Electric | Wholesale off-system
Operating revenues
% of revenue (as a percent)	3.10%
Electric | Miscellaneous sources, primarily public authorities
Operating revenues
% of revenue (as a percent)	2.70%
Electric | Other electric revenues
Operating revenues
% of revenue (as a percent)	1.70%
Other
Operating revenues
% of revenue (as a percent)	1.20%