Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Income from continuing operations before income taxes		$ 774	$ 886	$ 826
Income tax expense at statutory rate		163	310	289
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect		46	26	37
Accelerated flow-through of regulatory tax benefits2		(39)	(39)	(39)
TCJA excess deferred taxes		(26)	0	0
Production tax credits		(14)	(8)	(9)
Research and development tax credits, net		(11)	(1)	(2)
Impact of the TCJA		(4)	148	0
Other, net		0	(12)	(3)
Tax expense		$ 115	$ 424	$ 273
Effective tax rate		14.90%	47.90%	33.10%
Income tax benefit			$ 14
Valuation allowance		$ 8	15
Consumers Energy Company
Income Taxes [Line Items]
Income from continuing operations before income taxes		847	971	$ 936
Income tax expense at statutory rate		178	340	328
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect		51	30	44
Accelerated flow-through of regulatory tax benefits2		(39)	(39)	(39)
TCJA excess deferred taxes		(26)	0	0
Production tax credits		(12)	(8)	(9)
Research and development tax credits, net		(11)	(1)	(2)
Impact of the TCJA		1	33	0
Other, net		0	(16)	(2)
Tax expense		$ 142	$ 339	$ 320
Effective tax rate		16.80%	34.90%	34.20%
Reduction of income tax expense		$ 39	$ 39	$ 39
Net regulatory tax liability		3,836	3,795
Plant, property, and equipment (subject to normalization) | Consumers Energy Company
Increase (decrease) in income taxes from:
Net regulatory tax liability			$ 1,800
Revenue Subject To Refund Tax Reform Dfit Change | Consumers Energy Company
Increase (decrease) in income taxes from:
Net regulatory tax liability		35
Research Tax Credit Carryforward | Consumers Energy Company
Increase (decrease) in income taxes from:
Increase in tax credit carryforward	$ 8
Eliminate Write Off of Alternative Minimum Tax Credits
Increase (decrease) in income taxes from:
Valuation allowance		$ 9