Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Regulatory assets	$ 1,932	$ 1,956
Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Regulatory assets	1,932	1,956
Bay Harbor [Member]
Loss Contingencies [Line Items]
Environmental remediation permit renewal term	5 years
Demand for payment by USEPA	8
Cumulative environmental charge	246
Accrual for environmental loss contingencies	61
Discounted projected costs rate	4.34%
Remaining undiscounted obligation amount	78
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	9
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	115
Discounted projected costs rate	2.57%
Remaining undiscounted obligation amount	131
Number of former MGPs	23
Regulatory assets	145
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	4
Remediation and other response activity costs, minimum	4
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	$ 142
Gas Index Price Reporting [Member]
Loss Contingencies [Line Items]
Number of lawsuits	5