RATE MATTERS AND REGULATION - Regulatory Matters Asset (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets	$ 1,972.2	$ 2,061.8
Less: current portion	(231.7)	(303.9)
Total noncurrent regulatory assets	1,740.5	1,757.9
Pension and post-retirement costs
Regulatory Assets [Line Items]
Regulatory Assets	795.9	808.2
Debt reacquisition costs
Regulatory Assets [Line Items]
Regulatory Assets	105.8	113.5
Debt fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	112.0	134.5
Asset retirement obligations fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	114.3	111.4
Depreciation
Regulatory Assets [Line Items]
Regulatory Assets	55.3	58.0
Cost of removal
Regulatory Assets [Line Items]
Regulatory Assets	129.3	102.4
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	167.1	171.9
Analog meter unrecovered investment
Regulatory Assets [Line Items]
Regulatory Assets	29.9	35.6
Treasury yield hedges
Regulatory Assets [Line Items]
Regulatory Assets	22.6	23.7
Iatan No. 1 and common facilities
Regulatory Assets [Line Items]
Regulatory Assets	7.1	7.4
Iatan No. 2 construction accounting costs
Regulatory Assets [Line Items]
Regulatory Assets	26.1	26.8
Kansas property tax surcharge
Regulatory Assets [Line Items]
Regulatory Assets	21.7	33.1
Disallowed plant costs
Regulatory Assets [Line Items]
Regulatory Assets	14.8	15.0
La Cygne environmental costs
Regulatory Assets [Line Items]
Regulatory Assets	13.7	14.8
Deferred customer programs
Regulatory Assets [Line Items]
Regulatory Assets	18.0	19.9
Fuel recovery mechanisms
Regulatory Assets [Line Items]
Regulatory Assets	34.7	91.2
Solar rebates
Regulatory Assets [Line Items]
Regulatory Assets	39.8	45.2
Transmission delivery charge
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.8
Wolf Creek outage
Regulatory Assets [Line Items]
Regulatory Assets	31.0	21.8
Pension and other post-retirement benefit non-service costs
Regulatory Assets [Line Items]
Regulatory Assets	31.8	13.6
Retired generation facilities
Regulatory Assets [Line Items]
Regulatory Assets	130.5	159.9
Merger transition costs
Regulatory Assets [Line Items]
Regulatory Assets	42.3	47.0
Other regulatory liabilities
Regulatory Assets [Line Items]
Regulatory Assets	28.5	6.1
Evergy Kansas Central
Regulatory Assets [Line Items]
Regulatory Assets	823.7	797.5
Less: current portion	(93.3)	(97.1)
Total noncurrent regulatory assets	730.4	700.4
Evergy Kansas Central | Pension and post-retirement costs
Regulatory Assets [Line Items]
Regulatory Assets	359.9	343.7
Evergy Kansas Central | Debt reacquisition costs
Regulatory Assets [Line Items]
Regulatory Assets	97.3	104.1
Evergy Kansas Central | Debt fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Asset retirement obligations fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Depreciation
Regulatory Assets [Line Items]
Regulatory Assets	55.3	58.0
Evergy Kansas Central | Cost of removal
Regulatory Assets [Line Items]
Regulatory Assets	94.4	65.7
Evergy Kansas Central | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	52.8	49.5
Evergy Kansas Central | Analog meter unrecovered investment
Regulatory Assets [Line Items]
Regulatory Assets	29.9	35.6
Evergy Kansas Central | Treasury yield hedges
Regulatory Assets [Line Items]
Regulatory Assets	22.6	23.7
Evergy Kansas Central | Iatan No. 1 and common facilities
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Iatan No. 2 construction accounting costs
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Kansas property tax surcharge
Regulatory Assets [Line Items]
Regulatory Assets	18.7	23.7
Evergy Kansas Central | Disallowed plant costs
Regulatory Assets [Line Items]
Regulatory Assets	14.8	15.0
Evergy Kansas Central | La Cygne environmental costs
Regulatory Assets [Line Items]
Regulatory Assets	11.2	12.2
Evergy Kansas Central | Deferred customer programs
Regulatory Assets [Line Items]
Regulatory Assets	6.2	7.0
Evergy Kansas Central | Fuel recovery mechanisms
Regulatory Assets [Line Items]
Regulatory Assets	0.0	7.1
Evergy Kansas Central | Solar rebates
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Transmission delivery charge
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Wolf Creek outage
Regulatory Assets [Line Items]
Regulatory Assets	15.5	10.9
Evergy Kansas Central | Pension and other post-retirement benefit non-service costs
Regulatory Assets [Line Items]
Regulatory Assets	7.4	5.2
Evergy Kansas Central | Retired generation facilities
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Kansas Central | Merger transition costs
Regulatory Assets [Line Items]
Regulatory Assets	20.3	22.6
Evergy Kansas Central | Other regulatory liabilities
Regulatory Assets [Line Items]
Regulatory Assets	17.4	13.5
Evergy Metro
Regulatory Assets [Line Items]
Regulatory Assets	559.8	626.1
Less: current portion	(95.4)	(130.9)
Total noncurrent regulatory assets	464.4	495.2
Evergy Metro | Pension and post-retirement costs
Regulatory Assets [Line Items]
Regulatory Assets	330.7	361.5
Evergy Metro | Debt reacquisition costs
Regulatory Assets [Line Items]
Regulatory Assets	7.5	8.2
Evergy Metro | Debt fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Asset retirement obligations fair value adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Depreciation
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Cost of removal
Regulatory Assets [Line Items]
Regulatory Assets	34.9	36.7
Evergy Metro | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	79.4	91.6
Evergy Metro | Analog meter unrecovered investment
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Treasury yield hedges
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Iatan No. 1 and common facilities
Regulatory Assets [Line Items]
Regulatory Assets	2.8	2.9
Evergy Metro | Iatan No. 2 construction accounting costs
Regulatory Assets [Line Items]
Regulatory Assets	13.1	13.5
Evergy Metro | Kansas property tax surcharge
Regulatory Assets [Line Items]
Regulatory Assets	3.0	9.4
Evergy Metro | Disallowed plant costs
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | La Cygne environmental costs
Regulatory Assets [Line Items]
Regulatory Assets	2.5	2.6
Evergy Metro | Deferred customer programs
Regulatory Assets [Line Items]
Regulatory Assets	8.3	8.0
Evergy Metro | Fuel recovery mechanisms
Regulatory Assets [Line Items]
Regulatory Assets	16.6	41.7
Evergy Metro | Solar rebates
Regulatory Assets [Line Items]
Regulatory Assets	9.0	13.9
Evergy Metro | Transmission delivery charge
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.8
Evergy Metro | Wolf Creek outage
Regulatory Assets [Line Items]
Regulatory Assets	15.5	10.9
Evergy Metro | Pension and other post-retirement benefit non-service costs
Regulatory Assets [Line Items]
Regulatory Assets	15.6	4.8
Evergy Metro | Retired generation facilities
Regulatory Assets [Line Items]
Regulatory Assets	0.0	0.0
Evergy Metro | Merger transition costs
Regulatory Assets [Line Items]
Regulatory Assets	15.6	17.3
Evergy Metro | Other regulatory liabilities
Regulatory Assets [Line Items]
Regulatory Assets	$ 5.3	$ 2.3