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Financial Instruments (Schedule Of Investment Securities) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Held to maturity Debt securities - Cost $ 10 $ 9
Held to maturity Debt securities - Unrealized Gains   1
Held to maturity Debt securities - Fair Value 10 10
CMS Energy Common Stock [Member] | Consumers Energy Company [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Available for sale - Cost 5 6
Available for sale - Unrealized Gains 24 26
Available for sale - Fair Value 29 32
DB SERP [Member] | Mutual Fund [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Available for sale - Cost 136 123
Available for sale - Unrealized Gains   3
Available for sale - Fair Value 136 126
DB SERP [Member] | Mutual Fund [Member] | Consumers Energy Company [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Available for sale - Cost 95 83
Available for sale - Unrealized Gains   2
Available for sale - Fair Value $ 95 $ 85