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Financial Instruments (Schedule of Investment Securities) (Details) (USD $) In Millions			6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Consumers Energy Company [Member] Supplemental Executive Retirement Plan [Member]	Jun. 30, 2011 Supplemental Executive Retirement Plan [Member]	Jun. 30, 2011 Consumers Energy Company [Member] Mutual Fund [Member]	Dec. 31, 2010 Consumers Energy Company [Member] Mutual Fund [Member]	Jun. 30, 2011 Mutual Fund [Member]	Dec. 31, 2010 Mutual Fund [Member]	Jun. 30, 2011 Consumers Energy Company [Member] State and Municipal Bonds [Member]	Dec. 31, 2010 Consumers Energy Company [Member] State and Municipal Bonds [Member]	Jun. 30, 2011 State and Municipal Bonds [Member]	Dec. 31, 2010 State and Municipal Bonds [Member]	Jun. 30, 2011 Consumers Energy Company [Member] CMS Energy Common Stock [Member]	Dec. 31, 2010 Consumers Energy Company [Member] CMS Energy Common Stock [Member]	Jun. 30, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]
Available for sale - cost					$ 58	$ 39	$ 89	$ 62					$ 7	$ 8
Available for sale - unrealized gains					1		1						24	26
Available for sale - unrealized losses
Available for sale - fair value	116	90	17	26	59	39	90	62	17	17	26	28	31	34	107	90
Available for sale State and municipal bonds - cost									17	17	26	28
Held to maturity Debt securities - cost	7	5
Held to maturity Debt securities - unrealized gains		1
Held to maturity Debt securities - unrealized losses
Held to maturity Debt securities - fair value	7	6
SERP Contributions			$ 20	$ 27