Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income	$ 630.0	$ 685.6	$ 546.0
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	880.1	861.7	618.8
Amortization of nuclear fuel	58.3	51.4	43.6
Amortization of deferred refueling outage	25.4	25.5	21.2
Amortization of corporate-owned life insurance	20.1	19.8	22.6
Non-cash compensation	16.0	16.3	29.9
Net deferred income taxes and credits	126.9	121.5	124.2
Allowance for equity funds used during construction	(17.2)	(2.2)	(3.1)
Payments for asset retirement obligations	(18.4)	(17.8)	(22.4)
Equity in earnings of equity method investees, net of income taxes	(8.3)	(9.8)	(5.4)
Income from corporate-owned life insurance	(8.2)	(29.6)	(2.3)
Other	0.8	(3.2)	(5.2)
Changes in working capital items:
Accounts receivable	(4.9)	(23.1)	265.1
Accounts receivable pledged as collateral	(21.0)	26.0	(185.0)
Fuel inventory and supplies	(22.3)	29.9	54.7
Prepaid expenses and other current assets	16.9	43.4	(128.1)
Accounts payable	134.3	16.9	56.7
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
Changes in other liabilities	(82.0)	(75.5)	(15.9)
Cash Flows from Operating Activities	1,753.8	1,749.0	1,497.8
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Additions to property, plant and equipment	(1,560.3)	(1,210.1)	(1,069.7)
Cash acquired from the merger with Great Plains Energy	0.0	0.0	1,154.2
Purchase of securities - trusts	(65.6)	(55.8)	(117.5)
Sale of securities - trusts	56.5	47.3	117.7
Investment in corporate-owned life insurance	(19.1)	(18.3)	(17.1)
Proceeds from investment in corporate-owned life insurance	65.9	161.7	6.8
Proceeds from settlement of interest rate swap	0.0	0.0	140.6
Other investing activities	(11.1)	(5.1)	(17.6)
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 term loan facility	0.0	1,000.0	0.0
Repayment of term loan facility	0.0	1,000.0	0.0
Collateralized short-term borrowings, net	21.0	(26.0)	185.0
Proceeds from long-term debt	888.8	2,372.7	290.9
Retirements of long-term debt	(251.1)	(701.1)	(395.8)
Retirements of long-term debt of variable interest entities	(32.3)	(30.3)	(28.5)
Payment for settlement of interest rate swap accounted for as a cash flow hedge	0.0	(69.8)	0.0
Borrowings against cash surrender value of corporate-owned life insurance	55.5	59.4	56.5
Repayment of borrowings against cash surrender value of corporate-owned life insurance	(54.8)	(127.5)	(3.9)
Cash dividends paid	(465.0)	(462.5)	(475.0)
Repurchase of common stock under repurchase plan	0.0	(1,628.7)	(1,042.3)
Distributions to shareholders of noncontrolling interests	0.0	(8.6)	0.0
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
CASH, CASH EQUIVALENTS AND RESTRICTED CASH:
Beginning of period	23.2	160.3	3.5
End of period	$ 144.9	$ 23.2	$ 160.3