FAIR VALUE MEASUREMENTS - NAV (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) fund extension	Dec. 31, 2019 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	$ 2.5	$ 3.3
Evergy Kansas Central | Alternative investments fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Evergy Kansas Central | Real estate securities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Evergy Kansas Central | Nuclear decommissioning trust:
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	40.4
Unfunded Commitments	2.5	3.3
Evergy Kansas Central | Core bond fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Evergy Kansas Central | Combination debt/equity/other fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Evergy Kansas Central | Rabbi trust:
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Other Evergy
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0.0	0.0
Domestic | Evergy Kansas Central | Equity securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	$ 2.5	3.3
NAV, number of funds | fund	5
NAV, number of funds making distributions | fund	3
Domestic | Evergy Kansas Central | Equity Securities - Fourth Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Length of settlement	15 years
NAV, number of extensions | extension	3
NAV, extension term	1 year
Domestic | Evergy Kansas Central | Equity Securities - Fifth Fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Length of settlement	15 years
Fair Value, Measurements, Recurring
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	$ 587.5	573.2
Total rabbi trust	45.5	45.5
Total Assets	646.0	628.6
Fair Value, Measurements, Recurring | Evergy Kansas Central
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	279.1	272.5
Total rabbi trust	31.8	31.7
Total Assets	310.9	304.2
Fair Value, Measurements, Recurring | Evergy Kansas Central | Alternative investments fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	20.2	23.9
Fair Value, Measurements, Recurring | Evergy Kansas Central | Real estate securities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	12.8	12.6
Fair Value, Measurements, Recurring | Evergy Kansas Central | Core bond fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	39.6	39.3
Total rabbi trust	25.3	25.3
Fair Value, Measurements, Recurring | Evergy Kansas Central | Combination debt/equity/other fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	18.2	16.4
Total rabbi trust	6.3	6.3
Fair Value, Measurements, Recurring | Other Evergy
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total rabbi trust	13.7	13.8
Fair Value, Measurements, Recurring | Domestic | Evergy Kansas Central | Equity securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	90.9	86.1
NAV | Fair Value, Measurements, Recurring
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	40.4	44.0
Total rabbi trust	44.7	44.9
Total Assets	85.1	88.9
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	40.4	44.0
Total rabbi trust	31.6	31.6
Total Assets	72.0	75.6
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Alternative investments fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	$ 20.2	23.9
Length of Settlement	65 days
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Real estate securities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	$ 12.8	12.6
Length of Settlement	65 days
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Nuclear decommissioning trust:
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust		44.0
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Core bond fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	$ 0.0	0.0
Total rabbi trust	25.3	25.3
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Combination debt/equity/other fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	0.0	0.0
Total rabbi trust	6.3	6.3
NAV | Fair Value, Measurements, Recurring | Evergy Kansas Central | Rabbi trust:
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total rabbi trust	31.6	31.6
NAV | Fair Value, Measurements, Recurring | Other Evergy
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total rabbi trust	13.1	13.3
NAV | Fair Value, Measurements, Recurring | Domestic | Evergy Kansas Central | Equity securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total nuclear decommissioning trust	$ 7.4	$ 7.5