Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income available to common stockholders
Net Income	$ 162	$ 210	$ 137	$ 243	$ 168	$ 207	$ 94	$ 213	$ 752	$ 682	$ 659
Income (loss) attributable to noncontrolling interests	4	(8)	1	0	1	0	1	0	(3)	2	2
Net Income Available to Common Stockholders	$ 158	$ 218	$ 136	$ 243	$ 167	$ 207	$ 93	$ 213	$ 755	$ 680	$ 657
Average common shares outstanding
Weighted average shares - basic (in shares)									285.0	283.0	282.2
Dilutive nonvested stock awards (in shares)									0.7	0.7	0.7
Dilutive forward equity sale contracts									0.6	0.6	0.0
Weighted average shares - diluted (in shares)									286.3	284.3	282.9
Basic net income per average common share available to common stockholders (in dollars per share)	$ 0.55	$ 0.76	$ 0.48	$ 0.86	$ 0.59	$ 0.73	$ 0.33	$ 0.75	$ 2.65	$ 2.40	$ 2.33
Diluted net income per average common share available to common stockholders (in dollars per share)	$ 0.55	$ 0.76	$ 0.48	$ 0.85	$ 0.58	$ 0.73	$ 0.33	$ 0.75	$ 2.64	$ 2.39	$ 2.32