Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 152	$ 674
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	112	622
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	136	104
Non-current liabilities	0	531
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	138	109
Non-current liabilities	0	517
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	440	344
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	377	290
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	10
Non-current liabilities	150	140
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	$ 110	$ 102