Income Taxes (Loss And Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Total tax attributes	$ 453
Consumers Energy Company [Member]
Operating Loss Carryforwards [Line Items]
Total tax attributes	101
Federal Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	855
Federal net operating loss carryforward, Tax Attribute	179
Federal Tax Authority [Member] | Consumers Energy Company [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	309
Federal net operating loss carryforward, Tax Attribute	65
Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	487
Local net operating loss carryforwards, Tax Attribute	5
Alternative Minimum Tax [Member]
Operating Loss Carryforwards [Line Items]
Tax credits, Gross Amount	137
Alternative minimum tax credits, Tax Attribute	137
General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credits, Gross Amount	130
General business credits, Tax Attribute	130
General Business Tax Credit Carryforward [Member] | Consumers Energy Company [Member]
Operating Loss Carryforwards [Line Items]
Tax credits, Gross Amount	34
General business credits, Tax Attribute	34
Charitable Contribution Carryover [Member]
Operating Loss Carryforwards [Line Items]
Charitable contribution carryforwards	8
Charitable contribution carryover, Tax Attribute	2
Charitable Contribution Carryover [Member] | Consumers Energy Company [Member]
Operating Loss Carryforwards [Line Items]
Charitable contribution carryforwards	8
Charitable contribution carryover, Tax Attribute	$ 2