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, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share - CMS Energy [Abstract]
Net Income	$ (2)		$ 172		$ 93		$ 199		$ 78		$ 186		$ 125		$ 164		$ 462	$ 553	$ 525
Less income attributable to noncontrolling interest	1				1				1				1				2	2	2
Net Income Available to Common Stockholders	$ (3)		$ 172		$ 92		$ 199		$ 77		$ 186		$ 124		$ 164		$ 460	$ 551	$ 523
Weighted average shares - basic																	280.0	277.9	275.6
Add dilutive nonvested stock awards																	0.8	1.0	0.9
Weighted average shares - diluted																	280.8	278.9	276.5
Basic	$ (0.01)	[1]	$ 0.61	[1]	$ 0.33	[1]	$ 0.71	[1]	$ 0.28	[1]	$ 0.67	[1]	$ 0.45	[1]	$ 0.59	[1]	$ 1.64	$ 1.99	$ 1.90
Diluted	$ (0.01)	[1]	$ 0.61	[1]	$ 0.33	[1]	$ 0.71	[1]	$ 0.28	[1]	$ 0.67	[1]	$ 0.45	[1]	$ 0.59	[1]	1.64	1.98	1.89
Dividends Declared Per Common Share																	$ 1.33	$ 1.24	$ 1.16

[1] The sum of the quarters may not equal annual EPS due to changes in the number of shares outstanding.