Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 674	$ 436
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	622	392
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	104	38
Non-current liabilities	531	303
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	109	49
Non-current liabilities	517	295
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	344	235
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	290	193
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	10
Non-current liabilities	140	130
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	$ 102	$ 94