Income Taxes (Loss And Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Operating Loss Carryforwards [Line Items]
General business credits	$ 245
Total tax attributes	483
Consumers Energy Company
Operating Loss Carryforwards [Line Items]
General business credits	49
Total tax attributes	216
Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	747
Federal net operating loss carryforwards	157
Federal Tax Authority | Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	505
Federal net operating loss carryforwards	106
State Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1,241
Local net operating loss carryforwards	78
State Tax Authority | Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1,026
Local net operating loss carryforwards	61
Local Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	346
Local net operating loss carryforwards	3
General business credits
Operating Loss Carryforwards [Line Items]
Tax credits	245
General business credits | Consumers Energy Company
Operating Loss Carryforwards [Line Items]
Tax credits	$ 49