Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Income from continuing operataions before income taxes		$ 886	$ 826	$ 796
Income tax expense at statutory rate		310	289	279
State and local income taxes, net of federal effect	[1]	26	37	39
Accelerated flow-through of regulatory tax benefits	[2]	(39)	(39)	(39)
Employee share-based awards		(6)	(7)
Impact of TCJA		148
Other, net		(15)	(7)	(8)
Income Tax Expense		$ 424	$ 273	$ 271
Effective tax rate		47.90%	33.10%	34.00%
Income tax benefit		$ 14
Consumers Energy Company [Member]
Income Taxes [Line Items]
Income from continuing operataions before income taxes		971	$ 936	$ 896
Income tax expense at statutory rate		340	328	314
State and local income taxes, net of federal effect	[1]	30	44	42
Accelerated flow-through of regulatory tax benefits	[2]	(39)	(39)	(39)
Employee share-based awards		(6)	(6)
Impact of TCJA		33
Other, net		(19)	(7)	(15)
Income Tax Expense		$ 339	$ 320	$ 302
Effective tax rate		34.90%	34.20%	33.70%
Income tax benefit		$ 14
Reduction of income tax expense		$ 39	$ 39	$ 39

[1] In September 2017, CMS Energy completed the evaluation of its methodology for the state apportionment of Consumers' electricity sales to MISO, taking into account recent state tax law developments in the electric utility sector. As a result, CMS Energy intends to amend state income tax filings for 2013 through 2016 to seek a refund of taxes previously paid. To recognize the anticipated refund and the impact of the expected lower effective tax rate on their deferred state tax liabilities, CMS Energy, including Consumers, recorded a $14 million income tax benefit in 2017. The $14 million income tax benefit was net of reserves for uncertain tax positions and primarily attributable to Consumers.

[2] 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 $39 million for each of the years ended December 31, 2017, 2016, and 2015.