Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 13	$ 31	$ 37
Interest expense	21	26	64	77
Expected return on plan assets	(36)	(35)	(110)	(104)
Amortization of Net loss	17	22	52	67
Amortization of Prior service cost (credit)	1		3	1
Net periodic cost (credit)	13	26	40	78
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	11	12	31	36
Interest expense	20	25	62	74
Expected return on plan assets	(35)	(34)	(107)	(101)
Amortization of Net loss	16	22	50	66
Amortization of Prior service cost (credit)	1		3	1
Net periodic cost (credit)	13	25	39	76
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	7	14	19
Interest expense	12	14	35	43
Expected return on plan assets	(22)	(23)	(65)	(68)
Amortization of Net loss	5	5	16	16
Amortization of Prior service cost (credit)	(10)	(10)	(31)	(31)
Net periodic cost (credit)	(10)	(7)	(31)	(21)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	7	13	19
Interest expense	12	14	34	42
Expected return on plan assets	(20)	(22)	(60)	(65)
Amortization of Net loss	5	6	16	17
Amortization of Prior service cost (credit)	(10)	(10)	(30)	(30)
Net periodic cost (credit)	$ (9)	$ (5)	$ (27)	$ (17)