Quarterly Financial And Common Stock Information (Details) - USD ($) $ / shares in Units, $ 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, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue		$ 1,778		$ 1,527		$ 1,449		$ 1,829		$ 1,640		$ 1,587		$ 1,371		$ 1,801		$ 6,583	$ 6,399	$ 6,456
Operating income		379		330		241		388		280		375		275		326		1,338	1,256	1,178
Net Income		(2)		172		93		199		78		186		125		164		462	553	525
Income Attributable to Noncontrolling Interests		1				1				1				1				2	2	2
Net income available to common stockholders		$ (3)		$ 172		$ 92		$ 199		$ 77		$ 186		$ 124		$ 164		$ 460	$ 551	$ 523
Basic Earnings Per Average Common Share		$ (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 Earnings Per Average Common Share		$ (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
CMS Energy [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating income																		$ (9)	$ (14)	$ (8)
Net income available to common stockholders																		460	551	523
Consumers Energy Company [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue		$ 1,686		$ 1,437		$ 1,362		$ 1,737		$ 1,550		$ 1,498		$ 1,293		$ 1,723		6,222	6,064	6,165
Operating income		363		308		222		359		279	[2]	356	[2]	254	[2]	308	[2]	1,252	1,197	1,139
Net Income		136		181		104		211		117		195		132		172		632	616	594
Preferred stock dividends		1				1				1				1				2	2	2
Net income available to common stockholder		$ 135		$ 181		$ 103		$ 211		$ 116		$ 195		$ 131		$ 172		$ 630	$ 614	$ 592
Maximum [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Share price	[3]	$ 50.55		$ 49.10		$ 48.25		$ 45.28		$ 42.15		$ 46.17		$ 45.86		$ 42.44		$ 50.55	$ 42.15
Minimum [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Share price	[3]	$ 45.97		$ 45.57		$ 44.82		$ 41.51		$ 39.49		$ 41.31		$ 39.38		$ 35.61		$ 45.97	$ 39.49

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

[2] Prior period amounts have been adjusted as required to reflect the implementation of ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. For further details on the adoption of this standard, see Note 2, New Accounting Standards.

[3] Based on New York Stock Exchange composite transactions.