Schedule I - Condensed Financial Information of Registrant (Statements of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Income	$ 417	$ 343	$ 240
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	104	(105)	(91)
Increase (decrease) in accounts payable	30	(7)	(50)
Net cash provided by operating activities	1,169	959	848
Net cash used in investing activities	(1,058)	(1,003)	(935)
Proceeds from bank loans and notes	375	1,400	1,218
Issuance of common stock	29	10	9
Retirement of bank loans and notes	413	878	1,154
Payment of common stock dividends	211	154	114
Payment of preferred stock dividends	0	8	11
Debt issuance costs and financing fees	10	15	35
Redemption of preferred stock	0	239	4
Increase (decrease) in notes payable	0	(40)	40
Net cash (used in) provided by financing activities	(199)	202	(35)
Net change in cash and temporary cash investments	(86)	157	(117)
Cash and Cash Equivalents, Beginning of Period	247	90	207
Cash and Cash Equivalents, End of Period	161	247	90
CMS Energy Corporation [Member]
Net Income	415	340	229
Equity earnings of subsidiaries	(510)	(464)	(310)
Dividends received from subsidiaries	474	358	340
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	(1)		(2)
Increase (decrease) in accounts payable		(16)	16
Change in other assets and liabilities	(71)	117	7
Net cash provided by operating activities	307	335	280
Investment in subsidiaries	(125)	(250)	(100)
Net cash used in investing activities	(125)	(250)	(100)
Proceeds from bank loans and notes	375	800	718
Issuance of common stock	29	8	9
Retirement of bank loans and notes	(376)	(396)	(788)
Payment of common stock dividends	(211)	(154)	(114)
Payment of preferred stock dividends		(8)	(11)
Debt issuance costs and financing fees	(6)	(11)	(5)
Redemption of preferred stock		(239)	(4)
Increase (decrease) in notes payable	7	(85)	15
Net cash (used in) provided by financing activities	$ (182)	$ (85)	$ (180)