Reportable Segments (Details) - USD ($) $ 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
Segment Reporting Information [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
Depreciation and amortization									933	881	811
Income from equity method investees									9	15	13
Interest charges									458	438	435
Income tax expense (benefit)									115	424	273
Net income (loss) available to common stockholders	108	169	139	241	(3)	172	92	199	657	460	551
Plant, property, and equipment, gross	24,400				22,506				24,400	22,506	21,010
Investments in equity method investees	69				64				69	64	65
Total assets	24,529				23,050				24,529	23,050	21,622
Capital expenditures									2,081	1,722	1,633
Consumers Energy Company
Segment Reporting Information [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
Depreciation and amortization									921	872	803
Interest charges									289	276	268
Income tax expense (benefit)									142	339	320
Net income available to common stockholder	130	$ 180	$ 151	$ 242	135	$ 181	$ 103	$ 211	703	630	614
Plant, property, and equipment, gross	23,963				22,318				23,963	22,318	20,838
Total assets	22,025				21,099				22,025	21,099	19,946
Capital expenditures									1,825	1,683	1,618
Other reconciling items
Segment Reporting Information [Line Items]
Operating Revenue									157	132	120
Depreciation and amortization									4	3	3
Interest charges									168	163	166
Income tax expense (benefit)									(29)	11	(57)
Net income (loss) available to common stockholders									(81)	(141)	(79)
Plant, property, and equipment, gross	42				38				42	38	30
Investments in equity method investees	0				0				0	0	3
Total assets	2,104				1,663				2,104	1,663	1,478
Capital expenditures									12	7	5
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									0
Interest charges									1	1	0
Income tax expense (benefit)									0	(2)	0
Net income available to common stockholder									(1)	2	1
Plant, property, and equipment, gross	17				17				17	17	15
Total assets	29				53				29	53	70
Capital expenditures									2	1	0
Electric Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									4,561	4,448	4,379
Depreciation and amortization									682	654	603
Interest charges									209	201	196
Income tax expense (benefit)									109	245	246
Net income (loss) available to common stockholders									535	455	458
Plant, property, and equipment, gross	16,027				15,221				16,027	15,221	14,540
Total assets	14,079				13,906				14,079	13,906	13,429
Capital expenditures									865	882	1,007
Electric Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									4,561	4,448	4,379
Depreciation and amortization									682	654	603
Interest charges									209	201	196
Income tax expense (benefit)									109	245	246
Net income available to common stockholder									535	455	458
Plant, property, and equipment, gross	16,027				15,221				16,027	15,221	14,540
Total assets	14,143				13,907				14,143	13,907	13,430
Capital expenditures									865	882	1,007
Gas Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									1,903	1,774	1,685
Depreciation and amortization									239	218	200
Interest charges									79	74	72
Income tax expense (benefit)									33	96	74
Net income (loss) available to common stockholders									169	173	155
Plant, property, and equipment, gross	7,919				7,080				7,919	7,080	6,283
Total assets	7,806				7,139				7,806	7,139	6,446
Capital expenditures									958	800	611
Gas Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									1,903	1,774	1,685
Depreciation and amortization									239	218	200
Interest charges									79	74	72
Income tax expense (benefit)									33	96	74
Net income available to common stockholder									169	173	155
Plant, property, and equipment, gross	7,919				7,080				7,919	7,080	6,283
Total assets	7,853				7,139				7,853	7,139	6,446
Capital expenditures									958	800	611
Enterprises | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									252	229	215
Depreciation and amortization									8	6	5
Income from equity method investees									9	15	13
Interest charges									2	0	1
Income tax expense (benefit)									2	72	10
Net income (loss) available to common stockholders									34	(27)	17
Plant, property, and equipment, gross	412				167				412	167	157
Investments in equity method investees	69				64				69	64	62
Total assets	$ 540				$ 342				540	342	269
Capital expenditures									246	$ 33	$ 10
Enterprises | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									$ 0