Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 12	$ 21	$ 24
Interest expense	22	26	43	51
Expected return on plan assets	(37)	(35)	(74)	(69)
Amortization of Net loss	18	22	35	45
Amortization of Prior service cost (credit)	1	1	2	1
Net periodic cost (credit)	14	26	27	52
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	12	20	24
Interest expense	21	24	42	49
Expected return on plan assets	(36)	(34)	(72)	(67)
Amortization of Net loss	17	22	34	44
Amortization of Prior service cost (credit)	1	1	2	1
Net periodic cost (credit)	13	25	26	51
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	6	9	12
Interest expense	11	14	23	29
Expected return on plan assets	(21)	(22)	(43)	(45)
Amortization of Net loss	6	6	11	11
Amortization of Prior service cost (credit)	(11)	(11)	(21)	(21)
Net periodic cost (credit)	(11)	(7)	(21)	(14)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6	9	12
Interest expense	11	14	22	28
Expected return on plan assets	(20)	(21)	(40)	(43)
Amortization of Net loss	5	5	11	11
Amortization of Prior service cost (credit)	(10)	(10)	(20)	(20)
Net periodic cost (credit)	$ (9)	$ (6)	$ (18)	$ (12)