Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Income from continuing operataions before income taxes	$ 796	$ 729	$ 756
Income tax expense at statutory rate	279	255	265
State and local income taxes, net of federal effect	39	36	37
Accelerated flow-through of regulatory tax benefits	(39)	(39)
Other, net	(8)	(2)
Income Tax Expense	$ 271	$ 250	$ 302
Effective income tax rate	34.00%	34.30%	39.90%
Consumers Energy Company [Member]
Income Taxes [Line Items]
Income from continuing operataions before income taxes	$ 896	$ 873	$ 880
Income tax expense at statutory rate	314	306	308
State and local income taxes, net of federal effect	42	42	43
Accelerated flow-through of regulatory tax benefits	(39)	(39)
Other, net	(15)	(3)	(5)
Income Tax Expense	$ 302	$ 306	$ 346
Effective income tax rate	33.70%	35.10%	39.30%