Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income available to common stockholders
Net Income	$ 342	$ 243
Loss attributable to noncontrolling interests	(7)	0
Net Income Available to Common Stockholders	$ 349	$ 243
Average common shares outstanding
Weighted average shares - basic (in shares)	288.6	283.3
Dilutive nonvested stock awards (in shares)	0.5	0.8
Dilutive forward equity sale contracts	0.0	1.1
Weighted average shares - diluted (in shares)	289.1	285.2
Basic net income per average common share available to common stockholders (in dollars per share)	$ 1.21	$ 0.86
Diluted net income per average common share available to common stockholders (in dollars per share)	$ 1.21	$ 0.85