Cash And Cash Equivalents (Schedule Of Restricted Cash Balances) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in investing activities	$ (1,354)	$ (1,398)
Cash and cash equivalents, including restricted amounts, end of period	173	368	$ 257	$ 288
Consumers Energy Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in investing activities	(1,278)	(1,301)
Cash and cash equivalents, including restricted amounts, end of period	$ 85	50	$ 152	$ 71
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in investing activities		7
Cash and cash equivalents, including restricted amounts, end of period		29
New Accounting Pronouncement, Early Adoption, Effect [Member] | Consumers Energy Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash used in investing activities		8
Cash and cash equivalents, including restricted amounts, end of period		$ 29