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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income available to common stockholders
Net income	$ 94	$ 140	$ 307	$ 381
Income Attributable to Noncontrolling Interests	1	1	1	1
Net Income Available to Common Stockholders	$ 93	$ 139	$ 306	$ 380
Average common shares outstanding
Weighted average shares - basic (in shares)	282.9	282.1	282.9	281.8
Dilutive nonvested stock awards (in shares)	0.6	0.5	0.6	0.6
Dilutive forward equity sale contracts (in shares)	0.5	0.0	0.3	0.0
Weighted average shares - diluted (in shares)	284.0	282.6	283.8	282.4
Net income per average common share available to common stockholders
Basic earnings per average common share (in dollars per share)	$ 0.33	$ 0.49	$ 1.08	$ 1.35
Diluted earnings per average common share (in dollars per share)	$ 0.33	$ 0.49	$ 1.08	$ 1.35