Quarterly Financial And Common Stock Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,829	$ 1,599	$ 1,492	$ 1,953	$ 1,778	$ 1,527	$ 1,449	$ 1,829	$ 6,873	$ 6,583	$ 6,399
Operating income	250	294	255	363	379	330	241	388	1,162	1,338	1,256
Net Income	109	169	140	241	(2)	172	93	199	659	462	553
Income attributable to noncontrolling interests	1	0	1	0	1	0	1	0	2	2	2
Net income (loss) available to common stockholders	$ 108	$ 169	$ 139	$ 241	$ (3)	$ 172	$ 92	$ 199	$ 657	$ 460	$ 551
Basic earnings per average common share (in dollars per share)	$ 0.38	$ 0.60	$ 0.49	$ 0.86	$ (0.01)	$ 0.61	$ 0.33	$ 0.71	$ 2.33	$ 1.64	$ 1.99
Diluted earnings per average common share (in dollars per share)	$ 0.38	$ 0.59	$ 0.49	$ 0.86	$ (0.01)	$ 0.61	$ 0.33	$ 0.71	$ 2.32	$ 1.64	$ 1.98
Consumers Energy Company
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Operating Revenue	$ 1,712	$ 1,502	$ 1,395	$ 1,855	$ 1,686	$ 1,437	$ 1,362	$ 1,737	$ 6,464	$ 6,222	$ 6,064
Operating income	231	271	229	334	363	308	222	359	1,065	1,252	1,197
Net Income	131	180	152	242	136	181	104	211	705	632	616
Preferred stock dividends	1	0	1	0	1	0	1	0	2	2	2
Net income available to common stockholder	$ 130	$ 180	$ 151	$ 242	$ 135	$ 181	$ 103	$ 211	$ 703	$ 630	$ 614