Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified							12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]	Dec. 31, 2009 Consumers Energy Company [Member]	Dec. 31, 2010 2009 Interest Dispute [Member]	Dec. 31, 2010 2009 Interest Dispute [Member] Consumers Energy Company [Member]	Dec. 31, 2010 2009 Audit [Member]	Dec. 31, 2010 Changes to Taxable Income [Member] 2009 Audit [Member]	Dec. 31, 2010 Decrease Operating Loss Carryforward [Member] 2009 Audit [Member]	Dec. 31, 2010 Increase Taxable Income [Member] 2009 Audit [Member]	Dec. 31, 2011 Increase Taxable Income [Member] 2010 Audit [Member]
Uncertain tax benefits	$ 4	$ 4	$ 8	$ 4	$ 3	$ 3
Accrued interest, less than	0	1	1	0	1	1
Results of IRS audit							6	4	15	132	82	50
Remaining interest balance							3	1
Expected number of months until settlement on tax credit claim													12
Research and development tax credit claim													$ 21