Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income available to common stockholders
Income from continuing operations	$ 153	$ 198	$ 614	$ 556
Loss attributable to noncontrolling interests	(6)	(8)	(18)	(7)
Preferred stock dividends	3	0	3	0
Income from continuing operations available to common stockholders – basic and diluted	$ 156	$ 206	$ 629	$ 563
Average common shares outstanding
Weighted average shares - basic (in shares)	289.1	285.6	288.9	284.8
Dilutive nonvested stock awards (in shares)	0.5	0.8	0.5	0.9
Dilutive forward equity sale contracts (in shares)	0.0	0.5	0.0	0.6
Weighted average shares - diluted (in shares)	289.6	286.9	289.4	286.3
Income from continuing operations per average common share available to common stockholders - Basic (in dollars per share)	$ 0.54	$ 0.72	$ 2.18	$ 1.98
Income from continuing operations per average common share available to common stockholders - Diluted (in dollars per share)	$ 0.54	$ 0.72	$ 2.18	$ 1.97