Retirement Benefits (Schedule Of Net Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified					3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Consumers Energy Company [Member]	Dec. 31, 2012 Consumers Energy Company [Member]	Jun. 30, 2013 Pension Plans, Defined Benefit [Member]	Jun. 30, 2012 Pension Plans, Defined Benefit [Member]	Jun. 30, 2013 Pension Plans, Defined Benefit [Member]	Jun. 30, 2012 Pension Plans, Defined Benefit [Member]	Jun. 30, 2013 Pension Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Pension Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2013 Pension Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Pension Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member] Consumers Energy Company [Member]
Service cost					$ 14	$ 12	$ 27	$ 24	$ 13	$ 11	$ 26	$ 23	$ 9	$ 8	$ 18	$ 16	$ 9	$ 8	$ 18	$ 16
Interest expense					23	25	47	50	23	24	46	48	19	20	38	41	18	20	36	40
Expected return on plan assets					(32)	(32)	(64)	(63)	(32)	(31)	(63)	(61)	(19)	(16)	(38)	(33)	(17)	(16)	(35)	(31)
Amortization of Net loss					24	19	48	38	24	19	47	37	10	12	21	23	10	12	21	23
Amortization of Prior service cost					1	2	2	3	1	2	2	3	(5)	(5)	(10)	(10)	(5)	(5)	(10)	(10)
Net periodic cost					$ 30	$ 26	$ 60	$ 52	$ 29	$ 25	$ 58	$ 50	$ 14	$ 19	$ 29	$ 37	$ 15	$ 19	$ 30	$ 38
Discount rate	5.10%	4.40%	5.10%	4.40%