This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Publisher AICPA

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+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

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- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

Financial Instruments (Schedule Of Investment Securities) (Details) (USD $) In Millions, unless otherwise specified					9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 CMS Energy Common Stock [Member] Consumers Energy Company [Member]	Dec. 31, 2011 CMS Energy Common Stock [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Supplemental Executive Retirement Plan [Member]	Sep. 30, 2012 Supplemental Executive Retirement Plan [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member]	Dec. 31, 2011 Supplemental Executive Retirement Plan [Member] Mutual Fund [Member]	Sep. 30, 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			$ 6	$ 7			$ 124	$ 113	$ 84	$ 74
Available for sale - Unrealized Gains			25	28			4		2
Available for sale - Fair Value			31	35			128	113	86	74
Held to maturity Debt securities - Cost	8	7
Held to maturity Debt securities - Unrealized Gains	1
Held to maturity Debt securities - Fair Value	9	7
SERP Contributions					$ 13	$ 9