Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($) item	Sep. 30, 2015 USD ($) item lawsuit	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Increase due to change in estimate		$ 68
Increase in ARO liability
Regulatory assets	$ 1,870	$ 1,870	$ 1,956
Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Increase due to change in estimate		$ 68
Increase in ARO liability
Regulatory assets	1,870	$ 1,870	$ 1,956
Bay Harbor [Member]
Loss Contingencies [Line Items]
Environmental remediation permit renewal term		5 years
Demand for payment by USEPA	8	$ 8
Cumulative environmental charge		247
Accrual for environmental loss contingencies	$ 59	$ 59
Discounted projected costs rate	4.34%	4.34%
Remaining undiscounted obligation amount	$ 75	$ 75
Accrual for environmental loss contingencies, inflation rate	1.00%	1.00%
CERCLA Liability [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 2	$ 2
Remediation and other response activity costs, minimum	2	2
Remediation and other response activity costs. maximum	8	8
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 112	$ 112
Discounted projected costs rate	2.57%	2.57%
Remaining undiscounted obligation amount	$ 126	$ 126
Number of former MGPs | item	23	23
Regulatory assets	$ 143	$ 143
Authorized recovery, collection period		10 years
Accrual for environmental loss contingencies, inflation rate	2.50%	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	5	$ 5
Remediation and other response activity costs, minimum	5	5
Remediation and other response activity costs. maximum	6	6
Gas Utility [Member] | NREPA [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	1	1
Remediation and other response activity costs. maximum	3	3
Equatorial Guinea Tax Claim [Member]
Loss Contingencies [Line Items]
Foreign government tax claim on sale	$ 142	$ 142
Gas Index Price Reporting [Member]
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit		5