Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 10	$ 24	$ 20
Interest expense	26	25	51	50
Expected return on plan assets	(35)	(34)	(69)	(68)
Amortization of Net loss	22	14	45	29
Amortization of Prior service cost (credit)	1	1	1	1
Net periodic cost (credit)	26	16	52	32
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	10	24	20
Interest expense	24	24	49	48
Expected return on plan assets	(34)	(33)	(67)	(66)
Amortization of Net loss	22	14	44	28
Amortization of Prior service cost (credit)	1	1	1	1
Net periodic cost (credit)	25	16	51	31
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5	12	10
Interest expense	14	14	29	28
Expected return on plan assets	(22)	(22)	(45)	(44)
Amortization of Net loss	6	1	11	1
Amortization of Prior service cost (credit)	(11)	(11)	(21)	(21)
Net periodic cost (credit)	(7)	(13)	(14)	(26)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5	12	10
Interest expense	14	14	28	27
Expected return on plan assets	(21)	(21)	(43)	(42)
Amortization of Net loss	5	1	11	2
Amortization of Prior service cost (credit)	(10)	(10)	(20)	(20)
Net periodic cost (credit)	$ (6)	$ (11)	$ (12)	$ (23)