Schedule I - Condensed Financial Information of Registrant (Condensed Statements of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Other operating expense									$ 1,225		$ 1,237		$ 1,206
General taxes									229		205		210
Total operating expenses									5,250		5,500		5,454
Operating Loss	212	343	260	188	174	316	207	306	1,003		1,003		978
Interest income									5		9		19
Total other income									8		18		43
Interest on long-term debt									372		396		394
Intercompany interest expense and other									21		23		40
Total interest charges									389		415		431
Income Before Income Taxes									622		606		590
Income Tax Benefit									245		191		224
Income From Continuing Operations	67	149	101	60	41	140	101	133	377		415		366
Income (Loss) From Discontinued Operations				7				2	7	[1]	2	[2]	(23)	[3]
Net Income	67	149	101	67	41	140	101	135	384		417		343
Charge for Deferred Issuance Costs on Preferred Stock													8
Preferred Stock Dividends													8
Net Income Available to Common Stockholders	67	148	100	67	41	139	100	135	382		415		324
CMS Energy [Member]
Other operating expense									(8)		(9)		(6)
General taxes											6
Total operating expenses									(8)		(3)		(6)
Operating Loss									(8)		(3)		(6)
Equity earnings of subsidiaries									477		510		464
Interest income									1		1		1
Other expense									(5)		(5)		(8)
Total other income									473		506		457
Interest on long-term debt									140		143		147
Intercompany interest expense and other									5		6		4
Total interest charges									145		149		151
Income Before Income Taxes									320		354		300
Income Tax Benefit									(62)		(61)		(50)
Income From Continuing Operations									382		415		350
Income (Loss) From Discontinued Operations													(10)
Net Income									382		415		340
Charge for Deferred Issuance Costs on Preferred Stock													8
Preferred Stock Dividends													8
Net Income Available to Common Stockholders									$ 382		$ 415		$ 324

[1] Includes an $11 million ($7 million net of tax) reversal of a loss on disposal due to the elimination of a liability associated with the 2003 sale of Panhandle.

[2] Includes an operating gain of $3 million related to a litigation settlement at CMS Viron.

[3] Includes an operating loss of $2 million ($1 million net of tax) at Exeter, whose assets and liabilities were reclassified as held for sale in 2009.