Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 12
Interest expense	21	25
Expected return on plan assets	(37)	(34)
Amortization of Net loss	17	23
Amortization of Prior service cost (credit)	1
Net periodic cost (credit)	13	26
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	12
Interest expense	21	25
Expected return on plan assets	(36)	(33)
Amortization of Net loss	17	22
Amortization of Prior service cost (credit)	1
Net periodic cost (credit)	13	26
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6
Interest expense	12	15
Expected return on plan assets	(22)	(23)
Amortization of Net loss	5	5
Amortization of Prior service cost (credit)	(10)	(10)
Net periodic cost (credit)	(10)	(7)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	6
Interest expense	11	14
Expected return on plan assets	(20)	(22)
Amortization of Net loss	6	6
Amortization of Prior service cost (credit)	(10)	(10)
Net periodic cost (credit)	$ (9)	$ (6)