Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
U.S. federal income tax rate		21.00%	35.00%
State and local income taxes, net of federal effect		5.70%	4.70%
Accelerated flow-through of regulatory tax benefits	[1]	(5.00%)	(4.30%)
TCJA excess deferred taxes	[2]	(2.90%)
Research and development tax credits, net	[3]	(2.80%)	(0.10%)
Production tax credits		(1.50%)	(1.00%)
Employee share-based awards		(0.60%)	(1.90%)
Other, net		0.30%	0.10%
Effective tax rate		14.20%	32.50%
Regulatory liability current		$ 134		$ 80
Consumers Energy Company [Member]
Income Taxes [Line Items]
U.S. federal income tax rate		21.00%	35.00%
State and local income taxes, net of federal effect		6.20%	4.50%
Accelerated flow-through of regulatory tax benefits	[1]	(4.80%)	(4.20%)
TCJA excess deferred taxes	[2]	(2.90%)
Research and development tax credits, net	[3]	(2.70%)	(0.10%)
Production tax credits		(1.10%)	(0.70%)
Employee share-based awards		(0.60%)	(1.70%)
Other, net		0.30%	(0.40%)
Effective tax rate		15.40%	32.40%
Reduction of income tax expense		$ 14	$ 13
Regulatory liability current		134		$ 80
Research Tax Credit Carryforward [Member] | Consumers Energy Company [Member]
Income Taxes [Line Items]
Increase in credit		8
Revenue Subject to Refund - Tax Reform DFIT Change [Member] | Consumers Energy Company [Member]
Income Taxes [Line Items]
Regulatory liability current		11
Plant, Property, And Equipment (Subject To Normalization) [Member] | Consumers Energy Company [Member]
Income Taxes [Line Items]
Regulatory liability current		$ 1,800

[1] In 2013, the MPSC issued an order authorizing Consumers to accelerate the flow-through to electric and gas customers of certain income tax benefits associated primarily with the cost of removal of plant placed in service before 1993. Consumers implemented this regulatory treatment beginning in 2014. This change, which also accelerates Consumers' recognition of the income tax benefits, reduced Consumers' income tax expense by $14 million for the three months ended March 31, 2018 and by $13 million for the three months ended March 31, 2017.

[2] In December 2017, Consumers remeasured its deferred tax assets and liabilities at the new federal tax rate enacted by the TCJA and recorded a $1.8 billion regulatory liability. This regulatory liability relates to the excess deferred taxes arising from accelerated tax depreciation on assets in rate base that are governed by normalization provisions of the U.S. Internal Revenue Code. The normalization provisions require that the excess deferred taxes be refunded to customers over the remaining average service life of the associated assets. In January 2018, Consumers began to reduce this regulatory liability by crediting income tax expense. Consumers has fully reserved for the eventual refund of these excess deferred taxes that it has credited to income tax expense in a separate regulatory liability established by reducing revenue, and will continue to do so until these benefits are passed on to customers in accordance with an MPSC order, expected to be issued in 2019. At March 31, 2018, this reserve for refund of these excess deferred taxes totaled $11 million.

[3] In March 2018, Consumers finalized a study of research and development tax credits for the tax years 2012 through 2016. As a result, Consumers recognized an $8 million increase in the credit, net of reserves for uncertain tax positions.