Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 789	$ 591
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	730	529
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	461	390
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	441	368
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	8	8
Non-current liabilities	143	142
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	5	5
Non-current liabilities	104	101
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	144	19
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current liabilities	$ 181	$ 55