Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 13	$ 30	$ 40
Interest expense	24	23	74	70
Expected return on plan assets	(33)	(32)	(101)	(96)
Amortization of Net loss	14	24	43	72
Amortization of Prior service cost (credit)		1	1	3
Net periodic cost (credit)	15	29	47	89
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	13	30	39
Interest expense	24	23	72	69
Expected return on plan assets	(33)	(31)	(99)	(94)
Amortization of Net loss	14	23	42	70
Amortization of Prior service cost (credit)		1	1	3
Net periodic cost (credit)	15	29	46	87
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	15	23
Interest expense	14	14	42	52
Expected return on plan assets	(22)	(20)	(66)	(58)
Amortization of Net loss	1	3	2	24
Amortization of Prior service cost (credit)	(10)	(10)	(31)	(20)
Net periodic cost (credit)	(12)	(8)	(38)	21
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	15	23
Interest expense	13	14	40	50
Expected return on plan assets	(20)	(19)	(62)	(54)
Amortization of Net loss		3	2	24
Amortization of Prior service cost (credit)	(10)	(10)	(30)	(20)
Net periodic cost (credit)	$ (12)	$ (7)	$ (35)	$ 23