Income Taxes (Loss And Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	$ 68
General business credits	184
Total tax attributes	385
Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Total tax attributes	64
Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	603
Deferred tax assets capital loss carryforwards	2
Federal net operating loss carryforward	126
Federal Tax Authority | Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	222
Federal net operating loss carryforward	47
State Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred tax assets capital loss carryforwards	1
Local Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, Gross Amount	406
Local net operating loss carryforwards	4
Alternative minimum tax credits
Operating Loss Carryforwards [Line Items]
Tax credits	68
Capital Loss Carryforward | Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credits	12
Capital Loss Carryforward | State Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credits	10
General business credits
Operating Loss Carryforwards [Line Items]
Tax credits	184
General business credits | Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Tax credits	17
General business credits	$ 17