Reportable Segments (Details) - USD ($) $ 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
Segment Reporting Information [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
Depreciation and amortization									1,048	992	933
Income from equity method investees									5	10	9
Interest charges									561	519	458
Income tax expense									133	147	115
Net income available to common stockholders	158	218	136	243	167	207	93	213	755	680	657
Plant, property, and equipment, gross	27,907				25,390				27,907	25,390	24,400
Investments in equity method investees	70				71				70	71	69
Assets	29,666				26,837				29,666	26,837	24,529
Capital expenditures									2,280	2,147	2,081
Consumers Energy Company
Segment Reporting Information [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
Depreciation and amortization									1,023	975	921
Interest charges									320	297	289
Income tax expense									173	185	142
Net income available to common stockholders	190	$ 230	$ 159	$ 235	205	$ 213	$ 97	$ 226	814	741	703
Plant, property, and equipment, gross	26,757				24,963				26,757	24,963	23,963
Assets	25,399				23,699				25,399	23,699	22,025
Capital expenditures									2,167	2,134	1,825
Other reconciling items
Segment Reporting Information [Line Items]
Depreciation and amortization									1	1	0
Interest charges									179	157	136
Income tax expense									(53)	(56)	(41)
Net income available to common stockholders									(154)	(144)	(119)
Plant, property, and equipment, gross	21				20				21	20	17
Assets	23				48				23	48	98
Capital expenditures									1	1	2
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Depreciation and amortization									1	1	0
Interest charges									1	1	1
Net income available to common stockholders									(1)	(1)	(1)
Plant, property, and equipment, gross	21				20				21	20	17
Assets	29				20				29	20	29
Capital expenditures									1	1	2
Electric Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									4,372	4,439	4,561
Depreciation and amortization									739	713	682
Interest charges									217	213	209
Income tax expense									115	134	109
Net income available to common stockholders									554	509	535
Plant, property, and equipment, gross	17,155				16,158				17,155	16,158	16,027
Assets	15,829				14,911				15,829	14,911	14,079
Capital expenditures									1,281	1,162	865
Electric Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									4,372	4,439	4,561
Depreciation and amortization									739	713	682
Interest charges									217	213	209
Income tax expense									115	134	109
Net income available to common stockholders									554	509	535
Plant, property, and equipment, gross	17,155				16,158				17,155	16,158	16,027
Assets	15,893				14,973				15,893	14,973	14,143
Capital expenditures									1,281	1,162	865
Gas Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									1,817	1,937	1,903
Depreciation and amortization									283	261	239
Interest charges									102	83	79
Income tax expense									58	51	33
Net income available to common stockholders									261	233	169
Plant, property, and equipment, gross	9,581				8,785				9,581	8,785	7,919
Assets	9,429				8,659				9,429	8,659	7,806
Capital expenditures									885	971	958
Gas Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue									1,817	1,937	1,903
Depreciation and amortization									283	261	239
Interest charges									102	83	79
Income tax expense									58	51	33
Net income available to common stockholders									261	233	169
Plant, property, and equipment, gross	9,581				8,785				9,581	8,785	7,919
Assets	9,477				8,706				9,477	8,706	7,853
Capital expenditures									885	971	958
Enterprises | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									229	248	252
Depreciation and amortization									20	14	8
Income from equity method investees									5	10	9
Interest charges									7	7	2
Income tax expense									(4)	2	2
Net income available to common stockholders									36	33	34
Plant, property, and equipment, gross	1,113				405				1,113	405	412
Investments in equity method investees	70				71				70	71	69
Assets	1,276				527				1,276	527	540
Capital expenditures									108	5	246
EnerBank | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue									262	221	157
Depreciation and amortization									5	3	4
Interest charges									56	59	32
Income tax expense									17	16	12
Net income available to common stockholders									58	49	38
Plant, property, and equipment, gross	37				22				37	22	25
Assets	$ 3,109				$ 2,692				3,109	2,692	2,006
Capital expenditures									$ 5	$ 8	$ 10