SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2011 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)	8.00%
Number of customers	44,000
Gas | Residential
Operating revenues
% of revenue (as a percent)	62.50%
Gas | Commercial
Operating revenues
% of revenue (as a percent)	26.90%
Gas | Industrial
Operating revenues
% of revenue (as a percent)	1.50%
Gas | Other electric revenues
Operating revenues
% of revenue (as a percent)	9.10%
Electric
Operating revenues
% of revenue (as a percent)	90.90%
Number of customers	166,000
Electric | Water
Operating revenues
% of revenue (as a percent)	0.30%
Electric | Missouri
Operating revenues
% of revenue (as a percent)	88.80%
Electric | Kansas
Operating revenues
% of revenue (as a percent)	5.30%
Electric | Arkansas
Operating revenues
% of revenue (as a percent)	2.80%
Electric | Oklahoma
Operating revenues
% of revenue (as a percent)	3.10%
Electric | Residential
Operating revenues
% of revenue (as a percent)	42.40%
Electric | Commercial
Operating revenues
% of revenue (as a percent)	30.10%
Electric | Industrial
Operating revenues
% of revenue (as a percent)	15.10%
Electric | Wholesale on-system
Operating revenues
% of revenue (as a percent)	3.70%
Electric | Wholesale off-system
Operating revenues
% of revenue (as a percent)	4.50%
Electric | Miscellaneous sources, primarily public authorities
Operating revenues
% of revenue (as a percent)	2.60%
Electric | Other electric revenues
Operating revenues
% of revenue (as a percent)	1.60%
Other.
Operating revenues
% of revenue (as a percent)	1.10%