Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) site lawsuit	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Regulatory assets	$ 1,764	$ 2,091
Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Regulatory assets	1,764	$ 2,091
Bay Harbor [Member]
Loss Contingencies [Line Items]
Demand for payment by USEPA	8
Accrual for environmental loss contingencies	$ 48
Discounted projected costs rate	4.34%
Remaining undiscounted obligation amount	$ 61
Accrual for environmental loss contingencies, inflation rate	1.00%
CERCLA Liability [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 3
CERCLA Liability [Member] | Minimum [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Remediation and other response activity costs	3
CERCLA Liability [Member] | Maximum [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Remediation and other response activity costs	8
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 88
Discounted projected costs rate	2.57%
Remaining undiscounted obligation amount	$ 96
Number of former MGPs | site	23
Regulatory assets	$ 142
Authorized recovery, collection period	10 years
Accrual for environmental loss contingencies, inflation rate	2.50%
Electric Utility [Member] | NREPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 3
Electric Utility [Member] | NREPA [Member] | Minimum [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Remediation and other response activity costs	3
Electric Utility [Member] | NREPA [Member] | Maximum [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Remediation and other response activity costs	4
Gas Utility [Member] | NREPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	1
Gas Utility [Member] | NREPA [Member] | Maximum [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	3
Equatorial Guinea Tax Claim [Member]
Loss Contingencies [Line Items]
Foreign government tax claim on sale	$ 152
Class Action Lawsuits [Member]
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit	4
Individual Lawsuits [Member]
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit	1
MCV PPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Remediation and other response activity costs	$ 270