Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 10
Interest expense	25	25
Expected return on plan assets	(34)	(34)
Amortization of Net loss	23	15
Net periodic cost (credit)	26	16
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	10
Interest expense	25	24
Expected return on plan assets	(33)	(33)
Amortization of Net loss	22	14
Net periodic cost (credit)	26	15
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5
Interest expense	15	14
Expected return on plan assets	(23)	(22)
Amortization of Net loss	5
Amortization of Prior service cost (credit)	(10)	(10)
Net periodic cost (credit)	(7)	(13)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5
Interest expense	14	13
Expected return on plan assets	(22)	(21)
Amortization of Net loss	6	1
Amortization of Prior service cost (credit)	(10)	(10)
Net periodic cost (credit)	$ (6)	$ (12)