Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) site lawsuit	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Increase due to change in estimate		$ 74
Regulatory assets		1,840	$ 1,956
Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Increase due to change in estimate		74
Regulatory assets		$ 1,840	$ 1,956
Bay Harbor [Member]
Loss Contingencies [Line Items]
Environmental remediation permit renewal term		5 years
Demand for payment by USEPA		$ 8
Accrual for environmental loss contingencies		$ 58
Discounted projected costs rate		4.34%
Remaining undiscounted obligation amount		$ 74
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
Remediation and other response activity costs, minimum		3
Remediation and other response activity costs, maximum		8
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 114
Discounted projected costs rate		2.57%
Remaining undiscounted obligation amount		$ 129
Number of former MGPs | site		23
Regulatory assets		$ 146
Authorized recovery, collection period		10 years
Accrual for environmental loss contingencies, inflation rate		2.50%
Coal Ash Disposal [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Increase due to change in estimate	$ 68
Electric Utility [Member] | NREPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 3
Remediation and other response activity costs, minimum		3
Remediation and other response activity costs, maximum		5
Gas Utility [Member] | NREPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		1
Remediation and other response activity costs, maximum		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