Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13	$ 10	$ 37	$ 30
Interest expense	26	24	77	74
Expected return on plan assets	(35)	(33)	(104)	(101)
Amortization of Net loss	22	14	67	43
Amortization of Prior service cost (credit)			1	1
Net periodic cost (credit)	26	15	78	47
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	10	36	30
Interest expense	25	24	74	72
Expected return on plan assets	(34)	(33)	(101)	(99)
Amortization of Net loss	22	14	66	42
Amortization of Prior service cost (credit)			1	1
Net periodic cost (credit)	25	15	76	46
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	5	19	15
Interest expense	14	14	43	42
Expected return on plan assets	(23)	(22)	(68)	(66)
Amortization of Net loss	5	1	16	2
Amortization of Prior service cost (credit)	(10)	(10)	(31)	(31)
Net periodic cost (credit)	(7)	(12)	(21)	(38)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	5	19	15
Interest expense	14	13	42	40
Expected return on plan assets	(22)	(20)	(65)	(62)
Amortization of Net loss	6		17	2
Amortization of Prior service cost (credit)	(10)	(10)	(30)	(30)
Net periodic cost (credit)	$ (5)	$ (12)	$ (17)	$ (35)