Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	$ (872)	$ (239)
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(793)	(179)
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(8)	(8)
Non-current (liabilities)	(148)	(124)
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(5)	(5)
Non-current (liabilities)	(106)	(88)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(113)
Non-current assets		95
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(150)
Non-current assets		53
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	(568)	(109)
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current (liabilities)	$ (532)	$ (86)