Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 712	$ 10	$ 252
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	690	7	$ 242
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	700	0
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	682	0
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	1	0
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits contributions	$ 1	$ 0