Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Unbilled receivables	$ 472		$ 494
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Unbilled receivables	472		$ 494
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	10	$ 9
Accounts Receivable | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 10	$ 9