Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 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	5.40%	4.70%
TCJA excess deferred taxes	(5.90%)	(4.30%)
Production tax credits	(5.10%)	(3.10%)
Accelerated flow-through of regulatory tax benefits	(3.30%)	(1.60%)
Research and development tax credits, net	(0.30%)	(2.30%)
Refund of alternative minimum tax sequestration	0.00%	(2.30%)
Other, net	0.40%	(0.30%)
Effective tax rate	12.20%	11.80%
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	(4.90%)	(3.60%)
Production tax credits	(3.20%)	(1.60%)
Accelerated flow-through of regulatory tax benefits	(3.00%)	(1.60%)
Research and development tax credits, net	(0.20%)	(1.90%)
Other, net	(0.30%)	(0.50%)
Effective tax rate	14.60%	16.80%
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