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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income available to common stockholders
Net income	$ 210	$ 207	$ 590	$ 514
Income (Loss) Attributable to Noncontrolling Interests	(8)	0	(7)	1
Net Income Available to Common Stockholders	$ 218	$ 207	$ 597	$ 513
Average common shares outstanding
Weighted average shares - basic (in shares)	285.6	283.0	284.8	282.9
Dilutive nonvested stock awards (in shares)	0.8	0.8	0.9	0.8
Dilutive forward equity sale contracts (in shares)	0.5	0.8	0.6	0.5
Weighted average shares - diluted (in shares)	286.9	284.6	286.3	284.2
Net income per average common share available to common stockholders
Basic earnings per average common share (in dollars per share)	$ 0.76	$ 0.73	$ 2.10	$ 1.81
Diluted earnings per average common share (in dollars per share)	$ 0.76	$ 0.73	$ 2.09	$ 1.81