Contingencies and Commitments (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) facility	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)
Loss Contingencies [Line Items]
Environmental Loss Contingency, Statement Of Financial Position, Extensible Enumeration, Not Disclosed Flag	recorded liability
Regulatory assets	$ 3,608		$ 3,683
Consumers Energy Company
Loss Contingencies [Line Items]
Regulatory assets	3,608		$ 3,683
Consumers Energy Company | MGP sites
Loss Contingencies [Line Items]
Regulatory assets	$ 97
Consumers Energy Company | Ludington
Loss Contingencies [Line Items]
Ownership share	51.00%
Consumers Energy Company | Ludington Plant Overhaul Contract Dispute
Loss Contingencies [Line Items]
Damages sought		$ 15
Consumers Energy Company | J.H. Campbell 3 Plant Retirement Contract Dispute
Loss Contingencies [Line Items]
Damages sought		$ 37
Bay Harbor
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 44
Discount rate	4.34%
Accrual for environmental loss contingencies, inflation rate	1.00%
Accrual for environmental loss contingencies, gross	$ 56
NREPA | Electric Utility | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	4
NREPA | Minimum | Electric Utility | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	4
NREPA | Maximum | Electric Utility | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	5
CERCLA Liability | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	3
CERCLA Liability | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	3
CERCLA Liability | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	8
MGP sites | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 62
Number of former MGPs | facility	23
Regulatory asset collection period	10 years