Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017
Income Taxes [Line Items]
U.S. federal income tax rate	21.00%	21.00%
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect	4.70%	5.40%
TCJA excess deferred taxes	(4.00%)	(3.40%)
Production tax credits	(3.00%)	(2.50%)
Research and development tax credits, net	(1.50%)	(0.20%)
Alternative minimum tax sequestration	(1.30%)	0.00%
Accelerated flow-through of regulatory tax benefits	(1.50%)	(1.50%)
Other, net	(0.20%)	(1.20%)
Effective tax rate	14.20%	17.60%
AMT sequestration income tax benefit	$ 9
Consumers Energy Company
Income Taxes [Line Items]
U.S. federal income tax rate	21.00%	21.00%
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect	5.00%	5.70%
TCJA excess deferred taxes	(3.60%)	(3.20%)
Production tax credits	(1.90%)	(1.60%)
Research and development tax credits, net	(1.30%)	(0.20%)
Accelerated flow-through of regulatory tax benefits	(1.10%)	(1.00%)
Other, net	(0.30%)	(0.40%)
Effective tax rate	17.80%	20.30%
Reduction of income tax expense	$ 8	$ 7
Research Tax Credit Carryforward
Increase (decrease) in income taxes from:
Increase in credit	9
Research Tax Credit Carryforward | Consumers Energy Company
Increase (decrease) in income taxes from:
Increase in credit	$ 8
Plant, Property, And Equipment (Subject To Normalization) | Consumers Energy Company
Increase (decrease) in income taxes from:
Regulatory liabilities			$ 1,600