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, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share - CMS Energy [Abstract]
Net Income	$ 107		$ 148		$ 68		$ 202		$ 97		$ 94		$ 84		$ 204		$ 525	$ 479	$ 454
Less income attributable to noncontrolling interest	1				1				1				1				2	2	2
Net Income Available to Common Stockholders	$ 106		$ 148		$ 67		$ 202		$ 96		$ 94		$ 83		$ 204		$ 523	$ 477	$ 452
Weighted average shares - basic																	275.6	270.6	264.5
Add dilutive contingently convertible securities																		3.1	6.4
Add dilutive non-vested stock awards																	0.9	0.9	1.0
Weighted average shares - diluted																	276.5	274.6	271.9
Basic	$ 0.39	[1]	$ 0.53	[1]	$ 0.25	[1]	$ 0.73	[1]	$ 0.35	[1]	$ 0.34	[1]	$ 0.31	[1]	$ 0.77	[1]	$ 1.90	$ 1.76	$ 1.71
Diluted	$ 0.38	[1]	$ 0.53	[1]	$ 0.25	[1]	$ 0.73	[1]	$ 0.35	[1]	$ 0.34	[1]	$ 0.30	[1]	$ 0.75	[1]	1.89	1.74	1.66
Dividends declared per common share																	$ 1.16	$ 1.08	$ 1.02

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