Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($) lawsuit site	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Regulatory assets	$ 1,690	$ 1,764
Consumers Energy Company
Loss Contingencies [Line Items]
Regulatory assets	1,690	$ 1,764
Bay Harbor
Loss Contingencies [Line Items]
Demand for payment by USEPA	8
Accrual for obligations for environmental remediation	$ 47
Discounted projected costs rate	4.34%
Remaining undiscounted obligation amount	$ 58
Accrual for environmental loss contingencies, inflation rate	1.00%
Electric Utility | NREPA | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation	$ 3
Electric Utility | NREPA | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	3
Electric Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	4
Electric Utility | CERCLA Liability | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation	3
Electric Utility | CERCLA Liability | Minimum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	3
Electric Utility | CERCLA Liability | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	8
Gas Utility | NREPA | Maximum | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation	1
Remediation and other response activity costs	3
Gas Utility | Manufactured Gas Plant | Consumers Energy Company
Loss Contingencies [Line Items]
Accrual for obligations for environmental remediation	$ 83
Discounted projected costs rate	2.57%
Remaining undiscounted obligation amount	$ 90
Number of former MGPs | site	23
Regulatory assets	$ 139
Authorized recovery, collection period	10 years
Accrual for environmental loss contingencies, inflation rate	2.50%
Equatorial Guinea Tax Claim
Loss Contingencies [Line Items]
Foreign government tax claim on sale	$ 152
Class Action Lawsuits
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit	4
Individual Lawsuits
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit	1
MCV PPA | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	$ 270
Underwater cables Straits of Mackinac [Member] | Consumers Energy Company
Loss Contingencies [Line Items]
Remediation and other response activity costs	$ 10