Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Common Stock	Retained earnings	AOCI	Non-controlling interests
Beginning balance (in shares) at Dec. 31, 2017		142,094,275
Beginning balance at Dec. 31, 2017	$ 3,860.4	$ 2,734.8	$ 1,173.3	$ 0.0	$ (47.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	546.0		535.8		10.2
Issuance of stock to Great Plains Energy shareholders (in shares)		128,947,518
Issuance of stock to Great Plains Energy shareholders	6,979.9	$ 6,979.9
Issuance of restricted common stock (in shares)		122,505
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		533,273
Issuance of stock compensation and reinvested dividends, net of tax withholding	(16.7)	$ (16.7)
Dividends declared on common stock	(362.1)		(362.1)
Dividend equivalents declared	(1.0)		(1.0)
Stock compensation expense	29.9	$ 29.9
Repurchase of common stock (in shares)		(16,371,319)
Repurchase of common stock under repurchase plan	(1,042.3)	$ (1,042.3)
Derivative hedging activity, net of tax	(4.0)			(4.0)
Change in unrecognized pension expense, net of tax	1.0			1.0
Other	(0.4)	$ (0.4)
Ending balance (in shares) at Dec. 31, 2018		255,326,252
Ending balance at Dec. 31, 2018	9,990.7	$ 8,685.2	1,346.0	(3.0)	(37.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	685.6		669.9		15.7
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		111,849
Issuance of stock compensation and reinvested dividends, net of tax withholding	(2.4)	$ (2.4)
Dividends declared on common stock	(462.5)		(462.5)
Dividend equivalents declared	(1.9)		(1.9)
Stock compensation expense	16.3	$ 16.3
Repurchase of common stock (in shares)		(28,796,658)
Repurchase of common stock under repurchase plan	(1,628.7)	$ (1,628.7)
Consolidation of noncontrolling interests	3.8				3.8
Distributions to shareholders of noncontrolling interests	(8.6)				(8.6)
Derivative hedging activity, net of tax	(46.4)			(46.4)
Change in unrecognized pension expense, net of tax	(0.6)			(0.6)
Ending balance (in shares) at Dec. 31, 2019		226,641,443
Ending balance at Dec. 31, 2019	8,545.3	$ 7,070.4	1,551.5	(50.0)	(26.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	630.0		618.3		11.7
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		195,227
Issuance of stock compensation and reinvested dividends, net of tax withholding	(5.9)	$ (5.9)
Dividends declared on common stock	(465.0)		(465.0)
Dividend equivalents declared	(2.0)		(2.0)
Stock compensation expense	16.0	16.0
Derivative hedging activity, net of tax	3.0			3.0
Change in unrecognized pension expense, net of tax	(2.4)			(2.4)
Other	(0.5)	$ (0.5)
Ending balance (in shares) at Dec. 31, 2020		226,836,670
Ending balance at Dec. 31, 2020	$ 8,718.5	$ 7,080.0	$ 1,702.8	$ (49.4)	$ (14.9)