Financial Instruments (Schedule of Investment Securities) (Details) (USD $) In Millions, unless otherwise specified							3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Mar. 31, 2012 CMS Energy Common Stock [Member] Consumers Energy Company [Member]	Dec. 31, 2011 CMS Energy Common Stock [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Supplemental Executive Retirement Plan [Member]	Mar. 31, 2012 Supplemental Executive Retirement Plan [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member]	Dec. 31, 2011 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member]	Mar. 31, 2012 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member] Consumers Energy Company [Member]
Available for sale - cost					$ 5	$ 7			$ 126	$ 113	$ 85	$ 74
Available for sale - unrealized gains					24	28
Available for sale - unrealized losses
Available for sale - fair value	126	113	114	109	29	35			126	113	85	74
Held to maturity Debt securities - cost	8	7
Held to maturity Debt securities - unrealized gains	1
Held to maturity Debt securities - unrealized losses
Held to maturity Debt securities - fair value	9	7
SERP Contributions							$ 13	$ 9