Cash And Cash Equivalents (Schedule Of Cash And Cash Equivalents, Including Restricted Amounts) (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents		$ 323	$ 182
Restricted cash and cash equivalents	[1]	42	17
Other non-current assets	[1]	1	5
Cash and cash equivalents, including restricted amounts		366	204	$ 173	$ 257
Consumers Energy Company
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents		9	44
Restricted cash and cash equivalents	[1]	28	17
Other non-current assets		1	4
Cash and cash equivalents, including restricted amounts		$ 38	$ 65	$ 85	$ 152

[1] 1 All assets and liabilities were classified as Level 1 with the exception of some commodity contracts, which were classified as Level 3.