Schedule I - Condensed Financial Information of Registrant (Statements of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 384	$ 417	$ 343
Accounts and notes receivable	(147)	119	(72)
Accounts payable	(5)	30	(7)
Net cash provided by operating activities	1,241	1,169	959
Net cash used in investing activities	(1,350)	(1,058)	(1,003)
Proceeds from issuance of long-term debt	1,650	375	1,400
Issuance of common stock	30	29	10
Retirement of long-term debt	(1,527)	(413)	(878)
Payment of common stock dividends	(252)	(211)	(162)
Redemption of preferred stock			(239)
Increase (decrease) in notes payable	110		(40)
Net cash (used in) provided by financing activities	41	(199)	202
Net Increase (Decrease) in Cash and Cash Equivalents, Including Assets Held for Sale	(68)	(88)	158
Decrease (Increase) in Cash and Cash Equivalents Included in Assets Held for Sale		2	(1)
Net Increase in Cash and Cash Equivalents	(68)	(86)	157
Cash and Cash Equivalents, Beginning of Period	161	247	90
Cash and Cash Equivalents, End of Period	93	161	247
CMS Energy [Member]
Net Income	382	415	340
Equity earnings of subsidiaries	(477)	(510)	(464)
Dividends received from subsidiaries	401	474	358
Accounts and notes receivable	2	(1)
Accounts payable			(16)
Other current and non-current assets and liabilities	(30)	(71)	117
Net cash provided by operating activities	278	307	335
Investment in subsidiaries	(151)	(125)	(250)
Net cash used in investing activities	(151)	(125)	(250)
Proceeds from issuance of long-term debt	575	375	800
Issuance of common stock	30	29	8
Retirement of long-term debt	(463)	(376)	(396)
Payment of common stock dividends	(252)	(211)	(154)
Payment of preferred stock dividends			(8)
Redemption of preferred stock			(239)
Debt issuance costs and financing fees	(4)	(6)	(11)
Increase (decrease) in notes payable	(11)	7	(85)
Net cash (used in) provided by financing activities	(125)	(182)	(85)
Net Increase in Cash and Cash Equivalents	2
Cash and Cash Equivalents, End of Period	$ 2