Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	$ (239)	$ (1,451)
CMS Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	(19)	(24)
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	(179)	(1,385)
DB SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(8)	(7)
Non-current assets (liabilities)	(124)	(137)
DB SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Current assets (liabilities)	(5)	(4)
Non-current assets (liabilities)	(88)	(96)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	95	(682)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	53	(692)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	(109)	(627)
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-current assets (liabilities)	$ (86)	$ (590)