Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
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	5.50%	4.80%
TCJA excess deferred taxes	(5.80%)	(4.30%)
Production tax credits	(4.80%)	(3.30%)
Accelerated flow-through of regulatory tax benefits	(3.20%)	(1.60%)
Research and development tax credits, net	(0.30%)	(1.60%)
Refund of alternative minimum tax sequestration	0.00%	(1.40%)
Other, net	0.40%	0.10%
Effective tax rate	12.80%	13.70%
Refund of alternative minimum tax sequestration			$ (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	5.20%	5.00%
TCJA excess deferred taxes	(4.60%)	(3.60%)
Production tax credits	(3.50%)	(1.90%)
Accelerated flow-through of regulatory tax benefits	(2.20%)	(1.10%)
Research and development tax credits, net	(0.30%)	(1.30%)
Other, net	(0.20%)	(0.30%)
Effective tax rate	15.40%	17.80%
Research Tax Credit Carryforward
Increase (decrease) in income taxes from:
Increase (decrease) in tax credit carryforward			9
Research Tax Credit Carryforward | Consumers Energy Company
Increase (decrease) in income taxes from:
Increase (decrease) in tax credit carryforward			$ 8