RATE MATTERS AND REGULATION - Regulatory Matters Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 2,311.6	$ 2,329.0
Less: current portion	(63.3)	(110.2)
Total noncurrent regulatory liabilities	2,248.3	2,218.8
Taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,656.5	1,703.6
Deferred regulatory gain from sale leaseback
Regulatory Liabilities [Line Items]
Regulatory liabilities	53.6	59.1
Emission allowances
Regulatory Liabilities [Line Items]
Regulatory liabilities	50.1	54.1
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory liabilities	267.3	188.2
Pension and post-retirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	59.3	53.4
Jurisdictional allowance for funds used during construction
Regulatory Liabilities [Line Items]
Regulatory liabilities	28.7	30.3
La Cygne leasehold dismantling costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	29.6	29.5
Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities	49.1	48.1
Kansas tax credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	17.0	16.5
Purchase power agreement
Regulatory Liabilities [Line Items]
Regulatory liabilities	7.4	8.8
Merger customer credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	7.5
Fuel recovery mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities	34.1	0.0
Sibley AAO
Regulatory Liabilities [Line Items]
Regulatory liabilities	10.2	0.0
Refund of tax reform benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	70.9
Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities	48.7	59.0
Evergy Kansas Central
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,174.8	1,121.3
Less: current portion	(42.3)	(19.5)
Total noncurrent regulatory liabilities	1,132.5	1,101.8
Evergy Kansas Central | Taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities	856.4	853.2
Evergy Kansas Central | Deferred regulatory gain from sale leaseback
Regulatory Liabilities [Line Items]
Regulatory liabilities	53.6	59.1
Evergy Kansas Central | Emission allowances
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Kansas Central | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory liabilities	116.5	84.5
Evergy Kansas Central | Pension and post-retirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	31.5	28.3
Evergy Kansas Central | Jurisdictional allowance for funds used during construction
Regulatory Liabilities [Line Items]
Regulatory liabilities	28.7	30.3
Evergy Kansas Central | La Cygne leasehold dismantling costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	29.6	29.5
Evergy Kansas Central | Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Kansas Central | Kansas tax credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	17.0	16.5
Evergy Kansas Central | Purchase power agreement
Regulatory Liabilities [Line Items]
Regulatory liabilities	7.4	8.8
Evergy Kansas Central | Merger customer credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Kansas Central | Fuel recovery mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities	30.2	0.0
Evergy Kansas Central | Sibley AAO
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Kansas Central | Refund of tax reform benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	7.2
Evergy Kansas Central | Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.9	3.9
Evergy Metro
Regulatory Liabilities [Line Items]
Regulatory liabilities	803.6	847.1
Less: current portion	(11.4)	(52.8)
Total noncurrent regulatory liabilities	792.2	794.3
Evergy Metro | Taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities	568.9	609.2
Evergy Metro | Deferred regulatory gain from sale leaseback
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Emission allowances
Regulatory Liabilities [Line Items]
Regulatory liabilities	50.1	54.1
Evergy Metro | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory liabilities	150.8	103.7
Evergy Metro | Pension and post-retirement costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.3	25.1
Evergy Metro | Jurisdictional allowance for funds used during construction
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | La Cygne leasehold dismantling costs
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Kansas tax credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Purchase power agreement
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Merger customer credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	7.5
Evergy Metro | Fuel recovery mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Sibley AAO
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
Evergy Metro | Refund of tax reform benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	36.3
Evergy Metro | Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 13.5	$ 11.2