Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 14	$ 20	$ 27
Interest expense	25	23	50	47
Expected return on plan assets	(34)	(32)	(68)	(64)
Amortization of Net loss	14	24	29	48
Amortization of Prior service cost (credit)	1	1	1	2
Net periodic cost (credit)	16	30	32	60
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	13	20	26
Interest expense	24	23	48	46
Expected return on plan assets	(33)	(32)	(66)	(63)
Amortization of Net loss	14	24	28	47
Amortization of Prior service cost (credit)	1	1	1	2
Net periodic cost (credit)	16	29	31	58
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	9	10	18
Interest expense	14	19	28	38
Expected return on plan assets	(22)	(19)	(44)	(38)
Amortization of Net loss	1	10	1	21
Amortization of Prior service cost (credit)	(11)	(5)	(21)	(10)
Net periodic cost (credit)	(13)	14	(26)	29
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	9	10	18
Interest expense	14	18	27	36
Expected return on plan assets	(21)	(17)	(42)	(35)
Amortization of Net loss	1	10	2	21
Amortization of Prior service cost (credit)	(10)	(5)	(20)	(10)
Net periodic cost (credit)	$ (11)	$ 15	$ (23)	$ 30