New Accounting Standards (Schedule Of Restricted Cash Balances) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	$ 288	$ 249	$ 204
Cash from investing	(1,915)	(2,064)	(1,898)
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	257	288	249
CMS Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period
Cash from investing	(275)	(150)	(317)
Cash and Cash Equivalents, Including Restricted Amounts, End of Period
Consumers Energy Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	71	112	49
Cash from investing	(1,768)	(1,801)	(1,643)
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	152	71	112
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	22	42	32
Cash from investing		(20)	10
Cash and Cash Equivalents, Including Restricted Amounts, End of Period		22	42
New Accounting Pronouncement, Early Adoption, Effect [Member] | Consumers Energy Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	$ 21	41	31
Cash from investing		(20)	10
Cash and Cash Equivalents, Including Restricted Amounts, End of Period		$ 21	$ 41