Revenue (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 22	$ 30	$ 30
Unbilled receivables	486	437
Regulatory liabilities	146	151
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	22	33	29
Unbilled receivables	486	437
Regulatory liabilities	146	151
Consumers Energy Company | Reserve for customer refunds
Disaggregation of Revenue [Line Items]
Regulatory liabilities	2	28
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	22	33	29
Accounts Receivable | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 22	$ 33	$ 29