Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,778	$ 1,527	$ 1,449	$ 1,829	$ 1,640	$ 1,587	$ 1,371	$ 1,801	$ 6,583	$ 6,399	$ 6,456
Depreciation and amortization										881	811	750
Income (loss) from equity method investees	[1]									15	13	14
Interest charges										438	435	396
Income tax expense (benefit)										424	273	271
Net income available to common stockholders		(3)	172	92	199	77	186	124	164	460	551	523
Plant, property, and equipment, gross		22,506				21,010				22,506	21,010	18,943
Investments in equity method investees	[1]	64				65				64	65	64
Total Assets		23,050				21,622				23,050	21,622	20,299
Capital expenditures	[2]									1,722	1,633	1,741
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,686	1,437	1,362	1,737	1,550	1,498	1,293	1,723	6,222	6,064	6,165
Depreciation and amortization										872	803	744
Interest charges										276	268	250
Income tax expense (benefit)										339	320	302
Net income available to common stockholder		135	$ 181	$ 103	$ 211	116	$ 195	$ 131	$ 172	630	614	592
Plant, property, and equipment, gross		22,318				20,838				22,318	20,838	18,797
Total Assets		21,099				19,946				21,099	19,946	18,635
Capital expenditures	[2]									1,683	1,618	1,694
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,448	4,379	4,249
Depreciation and amortization										654	603	567
Interest charges										201	196	178
Income tax expense (benefit)										245	246	224
Net income available to common stockholders										455	458	437
Plant, property, and equipment, gross		15,221				14,540				15,221	14,540	13,059
Total Assets	[3]	13,906				13,429				13,906	13,429	12,660
Capital expenditures	[2]									882	1,007	1,136
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,448	4,379	4,249
Depreciation and amortization										654	603	567
Interest charges										201	196	178
Income tax expense (benefit)										245	246	224
Net income available to common stockholder										455	458	437
Plant, property, and equipment, gross		15,221				14,540				15,221	14,540	13,059
Total Assets	[3]	13,907				13,430				13,907	13,430	12,660
Capital expenditures	[2]									882	1,007	1,136
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,774	1,685	1,916
Depreciation and amortization										218	200	177
Interest charges										74	72	71
Income tax expense (benefit)										96	74	78
Net income available to common stockholders										173	155	154
Plant, property, and equipment, gross		7,080				6,283				7,080	6,283	5,723
Total Assets	[3]	7,139				6,446				7,139	6,446	5,912
Capital expenditures	[2]									800	611	558
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,774	1,685	1,916
Depreciation and amortization										218	200	177
Interest charges										74	72	71
Income tax expense (benefit)										96	74	78
Net income available to common stockholder										173	155	154
Plant, property, and equipment, gross		7,080				6,283				7,080	6,283	5,723
Total Assets	[3]	7,139				6,446				7,139	6,446	5,912
Capital expenditures	[2]									800	611	558
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue										229	215	190
Depreciation and amortization										6	5	4
Income (loss) from equity method investees	[1]									15	13	14
Interest charges											1
Income tax expense (benefit)										72	10	3
Net income available to common stockholders										(27)	17	4
Plant, property, and equipment, gross		167				157				167	157	120
Investments in equity method investees	[1]	64				62				64	62	61
Total Assets		342				269				342	269	270
Capital expenditures	[2]									33	10	44
Other reconciling items [Member]
Segment Reporting Information [Line Items]
Operating Revenue										132	120	101
Depreciation and amortization										3	3	2
Interest charges										163	166	147
Income tax expense (benefit)										11	(57)	(34)
Net income available to common stockholders										(141)	(79)	(72)
Plant, property, and equipment, gross		38				30				38	30	41
Investments in equity method investees	[1]					3					3	3
Total Assets		1,663				1,478				1,663	1,478	1,457
Capital expenditures	[2]									7	5	3
Other reconciling items [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Interest charges										1		1
Income tax expense (benefit)										(2)
Net income available to common stockholder										2	1	1
Plant, property, and equipment, gross		17				15				17	15	15
Total Assets		$ 53				$ 70				53	$ 70	$ 63
Capital expenditures										$ 1

[1] Consumers had no significant equity method investments.

[2] Amounts include purchase of capital lease additions. Amounts also include a portion of Consumers' capital expenditures for plant and equipment attributable to both the electric and gas utility businesses.

[3] Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.