Revenue (Components of Operating Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	$ 1,515	$ 1,343	$ 3,477	$ 3,101
Leasing income	40	35	86	74
Financing income	3	4	8	9
Total operating revenue	1,558	1,382	3,571	3,184
Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	1,158	1,020	2,289	2,045
Financing income	2	2	5	5
Total operating revenue	1,160	1,022	2,294	2,050
Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	332	306	1,133	1,020
Financing income	1	2	3	4
Total operating revenue	333	308	1,136	1,024
Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	25	17	55	36
Leasing income	40	35	86	74
Total operating revenue	65	52	141	110
Variable lease income	26	21	59	46
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	1,490	1,326	3,422	3,065
Financing income	3	4	8	9
Total operating revenue	1,493	1,330	3,430	3,074
Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	1,158	1,020	2,289	2,045
Financing income	2	2	5	5
Total operating revenue	1,160	1,022	2,294	2,050
Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	332	306	1,133	1,020
Financing income	1	2	3	4
Total operating revenue	333	308	1,136	1,024
Residential | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	781	713	1,903	1,687
Residential | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	561	507	1,129	988
Residential | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	220	206	774	699
Commercial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	449	392	957	880
Commercial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	390	341	735	680
Commercial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	59	51	222	200
Industrial | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	161	133	322	293
Industrial | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	153	126	291	266
Industrial | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	8	7	31	27
Other
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	25	17	55	36
Other | Enterprises | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	25	17	55	36
Other | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	99	88	240	205
Other | Consumers Energy Company | Electric Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	54	46	134	111
Other | Consumers Energy Company | Gas Utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue recognized from contracts with customers	$ 45	$ 42	$ 106	$ 94