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Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Pension And DB SERP [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 54 $ 49 $ 49
Interest expense 100 105 106
Expected return on plan assets (127) (125) (112)
Amortization of Net loss 101 79 65
Amortization of Prior service cost (credit) 3 5 5
Net periodic cost (credit) 131 113 113
Pension And DB SERP [Member] | Consumers Energy Company [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost 52 48 48
Interest expense 96 100 101
Expected return on plan assets (124) (122) (109)
Amortization of Net loss 98 77 63
Amortization of Prior service cost (credit) 3 5 5
Net periodic cost (credit) 125 108 108
OPEB [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost 29 32 27
Interest expense 65 82 77
Expected return on plan assets (77) (66) (66)
Amortization of Net loss 26 46 30
Amortization of Prior service cost (credit) (31) (20) (20)
Net periodic cost (credit) 12 74 48
OPEB [Member] | Consumers Energy Company [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost 28 31 26
Interest expense 63 79 74
Expected return on plan assets (72) (61) (61)
Amortization of Net loss 27 47 31
Amortization of Prior service cost (credit) (30) (20) (20)
Net periodic cost (credit) $ 16 $ 76 $ 50