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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)