RATE MATTERS AND REGULATION - Proceedings (Details) $ in Millions	1 Months Ended			3 Months Ended
	May 31, 2019 USD ($)	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Mar. 31, 2019
2018 Rate Case Proceedings | Westar Energy | Kansas Corporation Commission
Regulatory Proceedings [Line Items]
Refund percent on earnings over approved return on equity				0.5
Approved return on equity, percentage				9.30%
FERC 2019 TFR Proceeding | Westar Energy | Federal Energy Regulatory Commission
Regulatory Proceedings [Line Items]
Annual transmissions revenue estimated amount of increase (decrease) over prior year			$ (11.2)
FERC 2019 TFR Proceeding | KCP&L | Federal Energy Regulatory Commission
Regulatory Proceedings [Line Items]
Annual transmissions revenue estimated amount of increase (decrease) over prior year			$ (2.8)
Subsequent Event | Transmission Delivery Charge | Westar Energy | Kansas Corporation Commission
Regulatory Proceedings [Line Items]
Annual revenue decrease approved		$ 7.7
Scenario, Forecast | Subsequent Event | Transmission Delivery Charge | Westar Energy | Kansas Corporation Commission
Regulatory Proceedings [Line Items]
Annual transmissions revenue estimated amount of increase (decrease) over prior year	$ (8.3)