Revenue (Components of Operating Revenue) (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
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									$ 6,403	$ 6,502
Leasing income									174
Leasing income										160
Financing income									235	172
Consumers alternative-revenue programs									33	39
Total operating revenue	$ 1,795	$ 1,546	$ 1,445	$ 2,059	$ 1,829	$ 1,599	$ 1,492	$ 1,953	6,845	6,873	$ 6,583
Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									4,407	4,528
Financing income									9	10
Consumers alternative-revenue programs									23	23
Total operating revenue									4,439	4,561	4,448
Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,922	1,882
Financing income									5	5
Consumers alternative-revenue programs									10	16
Total operating revenue									1,937	1,903	1,774
Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									74	92
Leasing income									174
Leasing income										160
Total operating revenue									248	252	229
EnerBank | Operating Segments
Disaggregation of Revenue [Line Items]
Financing income									221	157
Total operating revenue									221	157	132
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									6,329	6,410
Financing income									14	15
Consumers alternative-revenue programs									33	39
Total operating revenue	$ 1,670	$ 1,429	$ 1,334	$ 1,943	$ 1,712	$ 1,502	$ 1,395	$ 1,855	6,376	6,464	6,222
Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									4,407	4,528
Financing income									9	10
Consumers alternative-revenue programs									23	23
Total operating revenue									4,439	4,561	4,448
Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,922	1,882
Financing income									5	5
Consumers alternative-revenue programs									10	16
Total operating revenue									1,937	1,903	$ 1,774
Consumers Energy Company | Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenue									0	0
Consumers Energy Company | EnerBank | Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenue									0	0
Residential | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									3,304	3,333
Residential | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,988	2,049
Residential | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,316	1,284
Commercial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,874	1,912
Commercial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									1,502	1,545
Commercial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									372	367
Industrial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									720	729
Industrial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									669	674
Industrial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									51	55
Other
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									74	92
Other | Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									74	92
Other | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									431	436
Other | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									248	260
Other | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers									$ 183	$ 176