Quarterly Financial And Common Stock Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,798	$ 1,575	$ 1,443	$ 1,864	$ 1,795	$ 1,546	$ 1,445	$ 2,059	$ 6,680	$ 6,845	$ 6,873
Operating income	352	369	273	368	311	351	218	359	1,362	1,239	1,162
Net Income	162	210	137	243	168	207	94	213	752	682	659
Income (loss) attributable to noncontrolling interests	4	(8)	1	0	1	0	1	0	(3)	2	2
Net income available to common stockholders	$ 158	$ 218	$ 136	$ 243	$ 167	$ 207	$ 93	$ 213	$ 755	$ 680	$ 657
Basic earnings per average common share (in dollars per share)	$ 0.55	$ 0.76	$ 0.48	$ 0.86	$ 0.59	$ 0.73	$ 0.33	$ 0.75	$ 2.65	$ 2.40	$ 2.33
Diluted earnings per average common share (in dollars per share)	$ 0.55	$ 0.76	$ 0.48	$ 0.85	$ 0.58	$ 0.73	$ 0.33	$ 0.75	$ 2.64	$ 2.39	$ 2.32
Consumers Energy Company
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,665	$ 1,450	$ 1,330	$ 1,744	$ 1,670	$ 1,429	$ 1,334	$ 1,943	$ 6,189	$ 6,376	$ 6,464
Operating income	308	338	246	329	308	319	175	328	1,221	1,130	1,065
Net Income	191	230	160	235	206	213	98	226	816	743	705
Preferred stock dividends	1	0	1	0	1	0	1	0	2	2	2
Net income available to common stockholders	$ 190	$ 230	$ 159	$ 235	$ 205	$ 213	$ 97	$ 226	$ 814	$ 741	$ 703