Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income available to common stockholders
Income from continuing operations	$ 153	$ 129	$ 461	$ 358
Income (loss) attributable to noncontrolling interests	(5)	1	(12)	1
Income from continuing operations available to common stockholders – basic and diluted	$ 158	$ 128	$ 473	$ 357
Average common shares outstanding
Weighted average shares - basic (in shares)	289.0	285.5	288.8	284.4
Dilutive nonvested stock awards (in shares)	0.4	0.6	0.5	0.7
Dilutive forward equity sale contracts	0.0	0.4	0.0	0.7
Weighted average shares - diluted (in shares)	289.4	286.5	289.3	285.8
Income from continuing operations per average common share available to common stockholders - Basic (in dollars per share)	$ 0.55	$ 0.45	$ 1.64	$ 1.25
Income from continuing operations per average common share available to common stockholders - Diluted (in dollars per share)	$ 0.55	$ 0.45	$ 1.64	$ 1.25