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, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share - CMS Energy [Abstract]
Net income	$ 78		$ 186		$ 125		$ 164		$ 107		$ 148		$ 68		$ 202		$ 553	$ 525	$ 479
Less income attributable to noncontrolling interest	1				1				1				1				2	2	2
Net Income Available to Common Stockholders	$ 77		$ 186		$ 124		$ 164		$ 106		$ 148		$ 67		$ 202		$ 551	$ 523	$ 477
Weighted average shares - basic																	277.9	275.6	270.6
Add dilutive contingently convertible securities																			3.1
Add dilutive non-vested stock awards																	1.0	0.9	0.9
Weighted average shares - diluted																	278.9	276.5	274.6
Basic	$ 0.28	[1]	$ 0.67	[1]	$ 0.45	[1]	$ 0.59	[1]	$ 0.39	[1]	$ 0.53	[1]	$ 0.25	[1]	$ 0.73	[1]	$ 1.99	$ 1.90	$ 1.76
Diluted	$ 0.28	[1]	$ 0.67	[1]	$ 0.45	[1]	$ 0.59	[1]	$ 0.38	[1]	$ 0.53	[1]	$ 0.25	[1]	$ 0.73	[1]	1.98	1.89	1.74
Dividends Declared Per Common Share																	$ 1.24	$ 1.16	$ 1.08

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