Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income from continuing operations before income taxes			$ 885	$ 829	$ 774
Income tax expense at statutory rate			186	174	163
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect			46	48	46
TCJA excess deferred taxes			(35)	(31)	(26)
Production tax credits			(28)	(20)	(14)
Accelerated flow-through of regulatory tax benefits			(13)	(13)	(39)
Research and development tax credits, net			(11)	(2)	(11)
Refund of alternative minimum tax sequestration			(9)	0	0
Other, net			(3)	(9)	(4)
Income tax expense			$ 133	$ 147	$ 115
Effective tax rate			15.00%	17.70%	14.90%
Increase (decrease) in tax credit carryforward			$ (7)
Consumers Energy Company
Income Taxes [Line Items]
Income from continuing operations before income taxes			989	$ 928	$ 847
Income tax expense at statutory rate			208	195	178
Increase (decrease) in income taxes from:
State and local income taxes, net of federal effect			47	53	51
TCJA excess deferred taxes			(35)	(31)	(26)
Production tax credits			(19)	(12)	(12)
Accelerated flow-through of regulatory tax benefits			(13)	(13)	(39)
Research and development tax credits, net			(11)	(2)	(11)
Other, net			(4)	(5)	1
Income tax expense			$ 173	$ 185	$ 142
Effective tax rate			17.50%	19.90%	16.80%
Net regulatory tax liability			$ 3,895	$ 3,829
Plant, property, and equipment (subject to normalization) | Consumers Energy Company
Increase (decrease) in income taxes from:
Net regulatory tax liability						$ 1,600
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	$ 8