Schedule I Financial Statements of Parent Company Statement of Cash Flows (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								7 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income attributable to Evergy, Inc.		$ 51.0	$ 364.5	$ 133.4	$ 69.4	$ 63.9	$ 366.8	$ 139.7	$ 99.5		$ 618.3	$ 669.9	$ 535.8
Adjustments to reconcile income to net cash from operating activities:
Non-cash compensation											16.0	16.3	29.9
Net deferred income taxes and credits											126.9	121.5	124.2
Equity in earnings from subsidiaries											(8.3)	(9.8)	(5.4)
Other											0.8	(3.2)	(5.2)
Changes in working capital items:
Prepaid expenses and other current assets											16.9	43.4	(128.1)
Accrued taxes											6.7	(8.2)	(76.4)
Other current liabilities											(98.9)	(59.4)	92.0
Changes in other assets											119.5	79.8	66.8
Cash Flows from Operating Activities											1,753.8	1,749.0	1,497.8
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Cash acquired from the merger with Great Plains Energy											0.0	0.0	1,154.2
Proceeds from settlement of interest rate swap											0.0	0.0	140.6
Cash Flows from (used in) Investing Activities											(1,533.7)	(1,080.3)	197.4
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Short-term debt, net											(246.9)	(176.7)	(104.0)
Proceeds from long-term debt											888.8	2,372.7	290.9
Payment for settlement of interest rate swap accounted for as a cash flow hedge	$ (69.8)										0.0	(69.8)	0.0
Cash dividends paid											(465.0)	(462.5)	(475.0)
Repurchase of common stock											0.0	(1,628.7)	(1,042.3)
Other financing activities											(13.6)	(6.7)	(21.3)
Cash Flows from (used in) Financing Activities											(98.4)	(805.8)	(1,538.4)
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH											121.7	(137.1)	156.8
Beginning of period					23.2				160.3		23.2	160.3	3.5
End of period		144.9				23.2				$ 160.3	144.9	23.2	160.3
Parent
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income attributable to Evergy, Inc.										324.9	612.5	664.4
Adjustments to reconcile income to net cash from operating activities:
Non-cash compensation										10.0	16.0	16.3
Net deferred income taxes and credits										(6.3)	9.6	21.4
Equity in earnings from subsidiaries										(364.7)	(683.4)	(698.2)
Other										0.0	7.0	2.1
Changes in working capital items:
Accounts receivable from subsidiaries										(8.5)	(30.0)	8.9
Income taxes receivable										(0.2)	0.6	(7.8)
Prepaid expenses and other current assets										(1.0)	0.8	(0.1)
Accounts payable to subsidiaries										4.7	5.0	(15.0)
Accrued taxes										(35.2)	0.0	0.0
Accrued interest										(13.6)	(0.7)	12.5
Other current liabilities										2.4	2.9	1.7
Cash dividends from subsidiaries										236.0	355.0	460.0
Changes in other assets										0.1	0.3	0.2
Changes in other liabilities										20.0	(3.7)	(3.5)
Cash Flows from Operating Activities										168.6	291.9	462.9
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Cash acquired from the merger with Great Plains Energy										1,142.2	0.0	0.0
Proceeds from settlement of interest rate swap										140.6	0.0	0.0
Cash Flows from (used in) Investing Activities										1,282.8	0.0	0.0
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Short-term debt, net										(56.1)	180.0	20.0
Proceeds from long-term debt										0.0	0.0	1,585.0
Payment for settlement of interest rate swap accounted for as a cash flow hedge										0.0	0.0	(69.8)
Cash dividends paid										(245.9)	(465.0)	(462.5)
Repurchase of common stock										(1,042.3)	0.0	(1,628.7)
Other financing activities										0.0	(7.5)	(2.4)
Cash Flows from (used in) Financing Activities										(1,344.3)	(292.5)	(558.4)
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH										107.1	(0.6)	(95.5)
Beginning of period					$ 11.6				$ 107.1	0.0	11.6	107.1
End of period		$ 11.0				$ 11.6				$ 107.1	$ 11.0	$ 11.6	$ 107.1