ORGANIZATION AND BASIS OF PRESENTATION - Pro Forma Financial Information (Details) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) $ / shares
Great Plains Energy
Business Acquisition [Line Items]
Operating revenues	$ 1,184.1
Net income attributable to Evergy, Inc.	$ 91.9
Basic earnings per common share (in dollars per share) \| $ / shares	$ 0.34
Diluted earnings per common share (in dollars per share) \| $ / shares	$ 0.34
Acquisition-related Costs
Business Acquisition [Line Items]
Merger-related, after tax costs	$ 5.2

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+ References

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