Cash And Cash Equivalents (Schedule Of Cash And Cash Equivalents, Including Restricted Amounts) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and cash equivalents	$ 182	$ 235
Restricted cash and cash equivalents	17	19
Other non-current assets	5	3
Cash and cash equivalents, including restricted amounts	204	257	$ 288	$ 249
Consumers Energy Company [Member]
Cash and cash equivalents	44	131
Restricted cash and cash equivalents	17	19
Other non-current assets	4	2
Cash and cash equivalents, including restricted amounts	$ 65	$ 152	$ 71	$ 112