Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 436	$ 766
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	392	711
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	38	143
Non-current liabilities	303	618
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	49	147
Non-current liabilities	295	602
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	9
Non-current liabilities	130	145
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	94	105
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	235	323
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	$ 193	$ 276