Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	$ (591)	$ (872)
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(529)	(793)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(390)	(568)
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(368)	(532)
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(8)	(8)
Non-current (liabilities)	(142)	(148)
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(5)	(5)
Non-current (liabilities)	(101)	(106)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(19)	(113)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	$ (55)	$ (150)