PENSION PLANS AND POST-RETIREMENT BENEFITS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	$ 2,718.2	$ 2,553.4
Service cost	78.9	79.1	$ 60.7
Interest cost	96.8	108.0	82.5
Contribution by participants	0.0	0.0
Plan amendments	4.2
Actuarial gain (loss)	273.9	262.4
Benefits paid	(202.5)	(180.5)
Settlements	(62.9)	96.6
Other	(5.5)	(7.6)
Defined benefit plan, benefit obligation, end of the year	2,901.1	2,718.2	2,553.4
Change in plan assets
Fair value of plan assets, beginning of the year	1,732.8	1,603.4
Actual return on plan assets	209.9	284.0
Contributions by employer and participants	123.4	125.2
Benefits paid	(198.6)	(175.6)
Settlements	(62.9)	(96.6)
Other	(5.5)	(7.6)
Fair value of plan assets, end of the year	1,799.1	1,732.8	1,603.4
Funded status at end of year	(1,102.0)	(985.4)
Amounts recognized in the consolidated balance sheets
Non-current asset	0.0	0.0
Current pension and other post-retirement liability	(4.4)	(5.6)
Noncurrent pension liability and other post-retirement liability	(1,097.6)	(979.8)
Net amount recognized before regulatory treatment	(1,102.0)	(985.4)
Accumulated OCI or regulatory asset/liability	566.9	454.1
Net amount recognized at December 31, 2020	(535.1)	(531.3)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	566.9	454.1
Pension Benefits | Evergy Kansas Central
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	1,323.4	1,258.9
Service cost	27.1	29.0	32.2
Interest cost	47.0	53.7	50.7
Contribution by participants	0.0	0.0
Plan amendments	8.1
Actuarial gain (loss)	127.0	120.3
Benefits paid	(102.3)	(136.9)
Settlements	0.0	0.0
Other	(0.7)	(1.6)
Defined benefit plan, benefit obligation, end of the year	1,429.6	1,323.4	1,258.9
Change in plan assets
Fair value of plan assets, beginning of the year	842.1	804.6
Actual return on plan assets	99.7	130.5
Contributions by employer and participants	45.8	43.0
Benefits paid	(99.9)	(134.4)
Settlements	0.0	0.0
Other	(0.7)	(1.6)
Fair value of plan assets, end of the year	887.0	842.1	804.6
Funded status at end of year	(542.6)	(481.3)
Amounts recognized in the consolidated balance sheets
Non-current asset	0.0	0.0
Current pension and other post-retirement liability	(2.5)	(3.0)
Noncurrent pension liability and other post-retirement liability	(540.1)	(478.3)
Net amount recognized before regulatory treatment	(542.6)	(481.3)
Accumulated OCI or regulatory asset/liability	408.0	354.9
Net amount recognized at December 31, 2020	(134.6)	(126.4)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	408.0	354.9
Pension Benefits | Evergy Metro
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	1,371.4	1,272.4
Service cost	51.8	50.1	48.6
Interest cost	49.1	53.3	49.9
Contribution by participants	0.0	0.0
Plan amendments	(3.9)
Actuarial gain (loss)	144.8	140.5
Benefits paid	(99.0)	(42.3)
Settlements	(62.9)	96.6
Other	(4.8)	(6.0)
Defined benefit plan, benefit obligation, end of the year	1,446.5	1,371.4	1,272.4
Change in plan assets
Fair value of plan assets, beginning of the year	890.7	798.8
Actual return on plan assets	110.2	153.5
Contributions by employer and participants	77.6	82.2
Benefits paid	(98.7)	(41.2)
Settlements	(62.9)	(96.6)
Other	(4.8)	(6.0)
Fair value of plan assets, end of the year	912.1	890.7	798.8
Funded status at end of year	(534.4)	(480.7)
Amounts recognized in the consolidated balance sheets
Non-current asset	0.0	0.0
Current pension and other post-retirement liability	(0.8)	(1.3)
Noncurrent pension liability and other post-retirement liability	(533.6)	(479.4)
Net amount recognized before regulatory treatment	(534.4)	(480.7)
Accumulated OCI or regulatory asset/liability	216.9	192.3
Net amount recognized at December 31, 2020	(317.5)	(288.4)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	216.9	192.3
Post-Retirement Benefits
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	264.3	249.3
Service cost	2.7	2.5	2.3
Interest cost	9.2	10.5	8.0
Contribution by participants	9.3	8.8
Plan amendments	1.0
Actuarial gain (loss)	19.6	20.9
Benefits paid	(25.7)	(27.7)
Settlements	0.0	0.0
Other	0.0	0.0
Defined benefit plan, benefit obligation, end of the year	280.4	264.3	249.3
Change in plan assets
Fair value of plan assets, beginning of the year	239.9	223.3
Actual return on plan assets	20.7	30.0
Contributions by employer and participants	11.7	13.2
Benefits paid	(24.0)	(26.6)
Settlements	0.0	0.0
Other	0.0	0.0
Fair value of plan assets, end of the year	248.3	239.9	223.3
Funded status at end of year	(32.1)	(24.4)
Amounts recognized in the consolidated balance sheets
Non-current asset	21.3	15.0
Current pension and other post-retirement liability	(1.6)	(1.9)
Noncurrent pension liability and other post-retirement liability	(51.8)	(37.5)
Net amount recognized before regulatory treatment	(32.1)	(24.4)
Accumulated OCI or regulatory asset/liability	4.0	(4.4)
Net amount recognized at December 31, 2020	(28.1)	(28.8)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	4.0	(4.4)
Post-Retirement Benefits | Evergy Kansas Central
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	138.7	133.6
Service cost	1.1	1.1	1.3
Interest cost	4.8	5.6	5.0
Contribution by participants	1.8	1.9
Plan amendments	0.5
Actuarial gain (loss)	11.0	9.5
Benefits paid	(11.1)	(13.0)
Settlements	0.0	0.0
Other	0.0	0.0
Defined benefit plan, benefit obligation, end of the year	146.8	138.7	133.6
Change in plan assets
Fair value of plan assets, beginning of the year	120.5	109.7
Actual return on plan assets	13.7	20.0
Contributions by employer and participants	2.1	3.5
Benefits paid	(10.5)	(12.7)
Settlements	0.0	0.0
Other	0.0	0.0
Fair value of plan assets, end of the year	125.8	120.5	109.7
Funded status at end of year	(21.0)	(18.2)
Amounts recognized in the consolidated balance sheets
Non-current asset	0.0	0.0
Current pension and other post-retirement liability	(0.8)	(1.0)
Noncurrent pension liability and other post-retirement liability	(20.2)	(17.2)
Net amount recognized before regulatory treatment	(21.0)	(18.2)
Accumulated OCI or regulatory asset/liability	1.0	(2.9)
Net amount recognized at December 31, 2020	(20.0)	(21.1)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	1.0	(2.9)
Post-Retirement Benefits | Evergy Metro
Components of net periodic benefit costs
Defined benefit plan, benefit obligation, beginning of the year	125.6	115.7
Service cost	1.6	1.4	2.0
Interest cost	4.4	4.9	4.8
Contribution by participants	7.5	6.9
Plan amendments	0.5
Actuarial gain (loss)	8.6	11.4
Benefits paid	(14.6)	(14.7)
Settlements	0.0	0.0
Other	0.0	0.0
Defined benefit plan, benefit obligation, end of the year	133.6	125.6	115.7
Change in plan assets
Fair value of plan assets, beginning of the year	119.4	113.6
Actual return on plan assets	7.0	10.0
Contributions by employer and participants	9.6	9.7
Benefits paid	(13.5)	(13.9)
Settlements	0.0	0.0
Other	0.0	0.0
Fair value of plan assets, end of the year	122.5	119.4	$ 113.6
Funded status at end of year	(11.1)	(6.2)
Amounts recognized in the consolidated balance sheets
Non-current asset	21.3	15.0
Current pension and other post-retirement liability	(0.9)	(0.9)
Noncurrent pension liability and other post-retirement liability	(31.5)	(20.3)
Net amount recognized before regulatory treatment	(11.1)	(6.2)
Accumulated OCI or regulatory asset/liability	(7.7)	(13.0)
Net amount recognized at December 31, 2020	(18.8)	(19.2)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Accumulated OCI or regulatory asset/liability	(7.7)	(13.0)
Actuarial (gain) loss | Pension Benefits
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	551.8	439.7
Actuarial (gain) loss | Pension Benefits | Evergy Kansas Central
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	388.9	342.3
Actuarial (gain) loss | Pension Benefits | Evergy Metro
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	218.6	189.4
Actuarial (gain) loss | Post-Retirement Benefits
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	2.2	(5.7)
Actuarial (gain) loss | Post-Retirement Benefits | Evergy Kansas Central
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	(0.3)	(4.2)
Actuarial (gain) loss | Post-Retirement Benefits | Evergy Metro
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	0.0	(4.9)
Prior service cost | Pension Benefits
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	15.1	14.4
Prior service cost | Pension Benefits | Evergy Kansas Central
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	19.1	12.6
Prior service cost | Pension Benefits | Evergy Metro
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	(1.7)	2.9
Prior service cost | Post-Retirement Benefits
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	1.8	1.3
Prior service cost | Post-Retirement Benefits | Evergy Kansas Central
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	1.3	1.3
Prior service cost | Post-Retirement Benefits | Evergy Metro
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Prior service cost	$ (7.7)	$ (8.1)