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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income available to common stockholders
Net Income	$ 109	$ 169	$ 140	$ 241	$ (2)	$ 172	$ 93	$ 199	$ 659	$ 462	$ 553
Income attributable to noncontrolling interests	1	0	1	0	1	0	1	0	2	2	2
Net Income Available to Common Stockholders	$ 108	$ 169	$ 139	$ 241	$ (3)	$ 172	$ 92	$ 199	$ 657	$ 460	$ 551
Average common shares outstanding
Weighted average shares - basic (in shares)									282.2	280.0	277.9
Dilutive nonvested stock awards (in shares)									0.7	0.8	1.0
Weighted average shares - diluted (in shares)									282.9	280.8	278.9
Basic net income per average common share available to common stockholders (in dollars per share)	$ 0.38	$ 0.60	$ 0.49	$ 0.86	$ (0.01)	$ 0.61	$ 0.33	$ 0.71	$ 2.33	$ 1.64	$ 1.99
Diluted net income per average common share available to common stockholders (in dollars per share)	$ 0.38	$ 0.59	$ 0.49	$ 0.86	$ (0.01)	$ 0.61	$ 0.33	$ 0.71	$ 2.32	$ 1.64	$ 1.98