Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Unbilled receivables	$ 321		$ 321		$ 663
Incentive revenue collection period	24 months		24 months
Consumers Energy Company
Disaggregation of Revenue [Line Items]
Unbilled receivables	$ 321		$ 321		$ 663
Accounts Receivable
Disaggregation of Revenue [Line Items]
Bad debt expense	15	$ 13	32	$ 31
Accounts Receivable | Consumers Energy Company
Disaggregation of Revenue [Line Items]
Bad debt expense	$ 15	$ 13	$ 32	$ 31