Reportable Segments (Details) - USD ($) $ 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
Segment Reporting Information [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
Depreciation and amortization									992	933	881
Income from equity method investees									10	9	15
Interest charges									519	458	438
Income tax expense (benefit)									147	115	424
Net income (loss) available to common stockholders	167	207	93	213	108	169	139	241	680	657	460
Plant, property, and equipment, gross	25,390				24,400				25,390	24,400	22,506
Investments in equity method investees	71				69				71	69	64
Total assets	26,837				24,529				26,837	24,529	23,050
Capital expenditures									2,147	2,081	1,722
Consumers Energy Company
Segment Reporting Information [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
Depreciation and amortization									975	921	872
Interest charges									297	289	276
Income tax expense (benefit)									185	142	339
Net income (loss) available to common stockholder	205	$ 213	$ 97	$ 226	130	$ 180	$ 151	$ 242	741	703	630
Plant, property, and equipment, gross	24,963				23,963				24,963	23,963	22,318
Total assets	23,699				22,025				23,699	22,025	21,099
Capital expenditures									2,134	1,825	1,683
Other reconciling items
Segment Reporting Information [Line Items]
Depreciation and amortization									1	0	0
Interest charges									157	136	144
Income tax expense (benefit)									(56)	(41)	(11)
Net income (loss) available to common stockholders									(144)	(119)	(169)
Plant, property, and equipment, gross	20				17				20	17	17
Total assets	48				98				48	98	210
Capital expenditures									1	2	1
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Depreciation and amortization									1	0	0
Interest charges									1	1	1
Income tax expense (benefit)									0	0	(2)
Net income (loss) available to common stockholder									(1)	(1)	2
Plant, property, and equipment, gross	20				17				20	17	17
Total assets	20				29				20	29	53
Capital expenditures									1	2	1
Electric Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									4,439	4,561	4,448
Depreciation and amortization									713	682	654
Interest charges									213	209	201
Income tax expense (benefit)									134	109	245
Net income (loss) available to common stockholders									509	535	455
Plant, property, and equipment, gross	16,158				16,027				16,158	16,027	15,221
Total assets	14,911				14,079				14,911	14,079	13,906
Capital expenditures									1,162	865	882
Electric Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									4,439	4,561	4,448
Depreciation and amortization									713	682	654
Interest charges									213	209	201
Income tax expense (benefit)									134	109	245
Net income (loss) available to common stockholder									509	535	455
Plant, property, and equipment, gross	16,158				16,027				16,158	16,027	15,221
Total assets	14,973				14,143				14,973	14,143	13,907
Capital expenditures									1,162	865	882
Gas Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									1,937	1,903	1,774
Depreciation and amortization									261	239	218
Interest charges									83	79	74
Income tax expense (benefit)									51	33	96
Net income (loss) available to common stockholders									233	169	173
Plant, property, and equipment, gross	8,785				7,919				8,785	7,919	7,080
Total assets	8,659				7,806				8,659	7,806	7,139
Capital expenditures									971	958	800
Gas Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									1,937	1,903	1,774
Depreciation and amortization									261	239	218
Interest charges									83	79	74
Income tax expense (benefit)									51	33	96
Net income (loss) available to common stockholder									233	169	173
Plant, property, and equipment, gross	8,785				7,919				8,785	7,919	7,080
Total assets	8,706				7,853				8,706	7,853	7,139
Capital expenditures									971	958	800
Enterprises | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									248	252	229
Depreciation and amortization									14	8	6
Income from equity method investees									10	9	15
Interest charges									7	2	0
Income tax expense (benefit)									2	2	72
Net income (loss) available to common stockholders									33	34	(27)
Plant, property, and equipment, gross	405				412				405	412	167
Investments in equity method investees	71				69				71	69	64
Total assets	527				540				527	540	342
Capital expenditures									5	246	33
Enterprises | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									0	0
EnerBank | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									221	157	132
Depreciation and amortization									3	4	3
Interest charges									59	32	19
Income tax expense (benefit)									16	12	22
Net income (loss) available to common stockholders									49	38	28
Plant, property, and equipment, gross	22				25				22	25	21
Total assets	$ 2,692				$ 2,006				2,692	2,006	1,453
Capital expenditures									8	10	$ 6
EnerBank | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									$ 0	$ 0