Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 252	$ 12	$ 108
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	242	8	$ 98
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	0	0
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	0	0
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	240	0
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 234	$ 0