Revenue (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 67	$ 54	$ 49
Unbilled receivables	426	409
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense			$ 29
Unbilled receivables	426	409
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	29	29
Accounts Receivable | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 29	$ 29