Quarterly Financial And Common Stock Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,795	$ 1,546	$ 1,445	$ 2,059	$ 1,829	$ 1,599	$ 1,492	$ 1,953	$ 6,845	$ 6,873	$ 6,583
Operating income	311	351	218	359	250	294	255	363	1,239	1,162	1,338
Net Income	168	207	94	213	109	169	140	241	682	659	462
Income attributable to noncontrolling interests	1	0	1	0	1	0	1	0	2	2	2
Net income (loss) available to common stockholders	$ 167	$ 207	$ 93	$ 213	$ 108	$ 169	$ 139	$ 241	$ 680	$ 657	$ 460
Basic earnings per average common share (in dollars per share)	$ 0.59	$ 0.73	$ 0.33	$ 0.75	$ 0.38	$ 0.60	$ 0.49	$ 0.86	$ 2.40	$ 2.33	$ 1.64
Diluted earnings per average common share (in dollars per share)	$ 0.58	$ 0.73	$ 0.33	$ 0.75	$ 0.38	$ 0.59	$ 0.49	$ 0.86	$ 2.39	$ 2.32	$ 1.64
Consumers Energy Company
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,670	$ 1,429	$ 1,334	$ 1,943	$ 1,712	$ 1,502	$ 1,395	$ 1,855	$ 6,376	$ 6,464	$ 6,222
Operating income	308	319	175	328	231	271	229	334	1,130	1,065	1,252
Net Income	206	213	98	226	131	180	152	242	743	705	632
Preferred stock dividends	1	0	1	0	1	0	1	0	2	2	2
Net income (loss) available to common stockholder	$ 205	$ 213	$ 97	$ 226	$ 130	$ 180	$ 151	$ 242	$ 741	$ 703	$ 630