Quarterly Financial And Common Stock Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,758		$ 1,430		$ 1,468		$ 2,523		$ 1,736		$ 1,445		$ 1,406		$ 1,979		$ 7,179		$ 6,566		$ 6,253
Operating Income (Loss)	273		236		235		408		264		317		232		329		1,152		1,142		1,003
Net Income	97		94		84		204		102		127		81		144		479		454		384
Income Attributable to Noncontrolling Interests	1				1						1		1				2		2		2
Net income attributable to CMS Energy	96		94		83		204		102		126		80		144		477		452		382
Basic Earnings Per Average Common Share	$ 0.35	[1]	$ 0.34	[1]	$ 0.31	[1]	$ 0.77	[1]	$ 0.38	[1]	$ 0.48	[1]	$ 0.30	[1]	$ 0.55	[1]	$ 1.76		$ 1.71		$ 1.46
Diluted Earnings Per Average Common Share	$ 0.35	[1]	$ 0.34	[1]	$ 0.30	[1]	$ 0.75	[1]	$ 0.37	[1]	$ 0.46	[1]	$ 0.29	[1]	$ 0.53	[1]	$ 1.74		$ 1.66		$ 1.42
CMS Energy [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Income (Loss)																	(6)		(6)		(8)
Net Income																	477		452		382
Net income attributable to CMS Energy																	477		452		382
Consumers Energy Company [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	1,672		1,359		1,387		2,382		1,674		1,386		1,342		1,919		6,800		6,321		6,013
Operating Income (Loss)	264		245		227		399		258		314		227		319		1,135		1,118		984
Net Income	118		119		109		221		119		153		100		162		567		534		439
Preferred stock dividends and distribution	1				1						1		1				2		2		2
Net Income Available to Common Stockholders	$ 117		$ 119		$ 108		$ 221		$ 119		$ 152		$ 99		$ 162		$ 565		$ 532		$ 437
Maximum [Member] | CMS Energy Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Share price	$ 36.42	[2]	$ 30.87	[2]	$ 31.15	[2]	$ 29.28	[2]	$ 28.05	[2]	$ 28.52	[2]	$ 29.94	[2]	$ 27.94	[2]	$ 36.42	[2]	$ 28.05	[2]
Minimum [Member] | CMS Energy Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Share price	$ 29.78		$ 28.18		$ 28.87		$ 26.12		$ 25.90	[2]	$ 25.86	[2]	$ 25.95	[2]	$ 24.76	[2]	$ 29.78		$ 25.90	[2]

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

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