Cash And Cash Equivalents (Schedule Of Cash And Cash Equivalents, Including Restricted Amounts) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Cash and cash equivalents	$ 142	$ 235
Restricted cash and cash equivalents	27	19
Other non-current assets	4	3
Cash and cash equivalents, including restricted amounts	173	257	$ 368	$ 288
Consumers Energy Company [Member]
Cash and cash equivalents	55	131
Restricted cash and cash equivalents	27	19
Other non-current assets	3	2
Cash and cash equivalents, including restricted amounts	$ 85	$ 152	$ 50	$ 71