Revenue (Components of Operating Revenue) (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
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									$ 6,238	$ 6,403	$ 6,502
Leasing income									148	174
Leasing income											160
Financing income									279	235	172
Consumers alternative-revenue programs									43	33	39
Consumers revenues to be refunded									(28)
Total operating revenue	$ 1,798	$ 1,575	$ 1,443	$ 1,864	$ 1,795	$ 1,546	$ 1,445	$ 2,059	6,680	6,845	6,873
Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									4,348	4,407	4,528
Financing income									11	9	10
Consumers alternative-revenue programs									29	23	23
Consumers revenues to be refunded									(16)
Total operating revenue									4,372	4,439	4,561
Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,809	1,922	1,882
Financing income									6	5	5
Consumers alternative-revenue programs									14	10	16
Consumers revenues to be refunded									(12)
Total operating revenue									1,817	1,937	1,903
Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									81	74	92
Leasing income									148	174
Leasing income											160
Total operating revenue									229	248	252
EnerBank | Operating Segments
Disaggregation of Revenue [Line Items]
Financing income									262	221	157
Total operating revenue									262	221	157
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									6,157	6,329	6,410
Financing income									17	14	15
Consumers alternative-revenue programs									43	33	39
Consumers revenues to be refunded									(28)
Total operating revenue	$ 1,665	$ 1,450	$ 1,330	$ 1,744	$ 1,670	$ 1,429	$ 1,334	$ 1,943	6,189	6,376	6,464
Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									4,348	4,407	4,528
Financing income									11	9	10
Consumers alternative-revenue programs									29	23	23
Consumers revenues to be refunded									(16)
Total operating revenue									4,372	4,439	4,561
Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,809	1,922	1,882
Financing income									6	5	5
Consumers alternative-revenue programs									14	10	16
Consumers revenues to be refunded									(12)
Total operating revenue									1,817	1,937	1,903
Residential | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									3,341	3,304	3,333
Residential | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									2,109	1,988	2,049
Residential | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,232	1,316	1,284
Commercial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,781	1,874	1,912
Commercial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,444	1,502	1,545
Commercial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									337	372	367
Industrial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									616	720	729
Industrial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									570	669	674
Industrial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									46	51	55
Other
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									81	74	92
Other | Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									81	74	92
Other | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									419	431	436
Other | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									225	248	260
Other | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									$ 194	$ 183	$ 176