Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 13
Interest expense	25	24
Expected return on plan assets	(34)	(32)
Amortization of Net loss	15	24
Amortization of Prior service cost (credit)		1
Net periodic cost (credit)	16	30
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	13
Interest expense	24	23
Expected return on plan assets	(33)	(31)
Amortization of Net loss	14	23
Amortization of Prior service cost (credit)		1
Net periodic cost (credit)	15	29
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	9
Interest expense	14	19
Expected return on plan assets	(22)	(19)
Amortization of Net loss		11
Amortization of Prior service cost (credit)	(10)	(5)
Net periodic cost (credit)	(13)	15
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	9
Interest expense	13	18
Expected return on plan assets	(21)	(18)
Amortization of Net loss	1	11
Amortization of Prior service cost (credit)	(10)	(5)
Net periodic cost (credit)	$ (12)	$ 15