Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	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		5.40%	5.70%
TCJA excess deferred taxes		(3.50%)	(2.90%)
Production tax credits		(2.40%)	(1.50%)
Accelerated flow-through of regulatory tax benefits		(1.50%)	(5.00%)
Research and development tax credits, net		(0.20%)	(2.80%)
Other, net		(0.40%)	(0.30%)
Effective tax rate		18.40%	14.20%
Regulatory liabilities, noncurrent		$ 3,736		$ 3,681
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		5.60%	6.20%
TCJA excess deferred taxes		(3.30%)	(2.90%)
Production tax credits		(1.00%)	(1.10%)
Accelerated flow-through of regulatory tax benefits		(2.50%)	(4.80%)
Research and development tax credits, net		(0.20%)	(2.70%)
Other, net		(0.30%)	(0.30%)
Effective tax rate		19.30%	15.40%
Reduction of income tax expense		$ 7	$ 14
Regulatory liabilities, noncurrent		3,736		$ 3,681
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					$ 1,800
TCJA Reserve For Refund | Consumers Energy Company
Increase (decrease) in income taxes from:
Regulatory liabilities, noncurrent		$ 48