Consolidated Statements Of Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Operating Revenue	$ 6,253		$ 6,503		$ 6,432
Operating Expenses
Fuel for electric generation	598		636		604
Purchased and interchange power	1,364		1,282		1,239
Purchased power - related parties	87		82		85
Cost of gas sold	1,150		1,512		1,590
Maintenance and other operating expenses	1,225		1,237		1,206
Depreciation and amortization	598		546		576
General taxes	229		205		210
Insurance settlement					(50)
Gain on asset sales, net	(1)				(6)
Total operating expenses	5,250		5,500		5,454
Operating Income	1,003		1,003		978
Other Income (Expense)
Interest income	5		9		19
Allowance for equity funds used during construction	8		6		5
Income from equity method investees	17		9		11
Other income	11		16		32
Other expense	(33)		(22)		(24)
Total other income	8		18		43
Interest Charges
Interest on long-term debt	372		396		394
Other interest expense	21		23		40
Allowance for borrowed funds used during construction	(4)		(4)		(3)
Total interest charges	389		415		431
Income Before Income Taxes	622		606		590
Income Tax Expense	245		191		224
Income From Continuing Operations	377		415		366
Income (Loss) From Discontinued Operations	7	[1]	2	[2]	(23)	[3]
Net Income	384		417		343
Income Attributable to Noncontrolling Interests	2		2		3
Net income attributable to CMS Energy	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
Net Income Attributable to Common Stockholders
Amounts attributable to continuing operations	375		413		347
Amounts attributable to discontinued operations	7		2		(23)
Net Income Available to Common Stockholders	382		415		324
Income Attributable to Noncontrolling Interests
Amounts attributable to continuing operations	2		2		3
Amounts attributable to discontinued operations
Income attributable to noncontrolling interests	2		2		3
Basic Earnings Per Average Common Share
Basic earnings from continuing operations	$ 1.43		$ 1.65		$ 1.50
Basic earnings (loss) from discontinued operations	$ 0.03		$ 0.01		$ (0.10)
Basic earnings attributable to common stock	$ 1.46		$ 1.66		$ 1.40
Diluted Earnings Per Average Common Share
Diluted earnings from continuing operations	$ 1.39		$ 1.57		$ 1.36
Diluted earnings (loss) from discontinued operations	$ 0.03		$ 0.01		$ (0.08)
Diluted earnings attributable to common stock	$ 1.42		$ 1.58		$ 1.28
Dividends Declared Per Common Share	$ 0.96		$ 0.84		$ 0.66
Consumers Energy Company [Member]
Operating Revenue	6,013		6,253		6,156
Operating Expenses
Fuel for electric generation	517		559		520
Purchased and interchange power	1,339		1,267		1,224
Purchased power - related parties	86		81		84
Cost of gas sold	1,110		1,438		1,516
Maintenance and other operating expenses	1,162		1,175		1,109
Depreciation and amortization	592		542		572
General taxes	223		206		205
Total operating expenses	5,029		5,268		5,230
Operating Income	984		985		926
Other Income (Expense)
Interest income	4		7		18
Interest and dividend income - related parties	1		2
Allowance for equity funds used during construction	8		6		5
Other income	16		19		31
Other expense	(33)		(20)		(15)
Total other income	(4)		14		39
Interest Charges
Interest on long-term debt	232		251		246
Other interest expense	16		18		34
Allowance for borrowed funds used during construction	(4)		(4)		(3)
Total interest charges	244		265		277
Income Before Income Taxes	736		734		688
Income Tax Expense	297		267		254
Net Income	439		467		434
Preferred Stock Dividends	2		2		2
Net Income Available to Common Stockholders	437		465		432
Net Income Attributable to Common Stockholders
Net Income Available to Common Stockholders	$ 437		$ 465		$ 432

[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.