Reportable Segments (Reconciliation of Revenue from Segments to Consolidated) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Operating Revenue	$ 1,620		$ 1,464	$ 1,364	$ 2,055	$ 1,682		$ 1,443	$ 1,340	$ 1,967	$ 6,503		$ 6,432		$ 6,205
Income (loss) from equity method investees											9	[1]	11	[1]	(2)	[1]
Other Depreciation and amortization											546		576		570
Interest Expense											415		431		435
Income Tax Expense Benefit											191		224		115
Total Net Income Available to Common Stockholders	41		139	100	135	25		134	80	85	415		324		218
Equity Method Investments	50	[1]				49	[1]				50	[1]	49	[1]	9	[1]
Plant And Property Gross	14,751					14,145					14,751		14,145		13,716
Total Assets	16,452	[2]				15,616	[2]				16,452	[2]	15,616	[2]	15,256	[2]
Capital Expenditures											928	[3]	883	[3]	834	[3]
Consumers Energy Company [Member]
Operating Revenue	1,565		1,397	1,303	1,988	1,620		1,370	1,276	1,890	6,253		6,156		5,963
Other Depreciation and amortization											542		572		559
Interest Expense											265		277		292
Income Tax Expense Benefit											267		254		163
Total Net Income Available to Common Stockholders	67		154	91	153	79		159	87	107	465		432		291
Plant And Property Gross	14,621					14,022					14,621		14,022		13,352
Total Assets	15,662	[2]				14,839	[2]				15,662	[2]	14,839	[2]	14,622	[2]
Capital Expenditures											922	[3]	877	[3]	827	[3]
Electric Utility [Member]
Operating Revenue											3,913		3,802		3,407
Other Depreciation and amortization											412		450		441
Interest Expense											192		202		225
Income Tax Expense Benefit											190		187		107
Total Net Income Available to Common Stockholders											333		303		194
Plant And Property Gross	10,400					9,944					10,400		9,944		9,525
Total Assets	9,938	[2]				9,321	[2]				9,938	[2]	9,321	[2]	9,157	[2]
Capital Expenditures											661	[3]	642	[3]	557	[3]
Electric Utility [Member] | Consumers Energy Company [Member]
Operating Revenue											3,913		3,802		3,407
Other Depreciation and amortization											412		450		441
Interest Expense											192		202		225
Income Tax Expense Benefit											190		187		107
Total Net Income Available to Common Stockholders											333		303		194
Plant And Property Gross	10,400					9,944					10,400		9,944		9,525
Total Assets	9,938	[2]				9,321	[2]				9,938	[2]	9,321	[2]	9,157	[2]
Capital Expenditures											661	[3]	642	[3]	557	[3]
Gas Utility [Member]
Operating Revenue											2,340		2,354		2,556
Other Depreciation and amortization											130		122		118
Interest Expense											71		73		66
Income Tax Expense Benefit											77		67		56
Total Net Income Available to Common Stockholders											130		127		96
Plant And Property Gross	4,206					4,063					4,206		4,063		3,812
Total Assets	4,956	[2]				4,614	[2]				4,956	[2]	4,614	[2]	4,594	[2]
Capital Expenditures											261	[3]	235	[3]	270	[3]
Gas Utility [Member] | Consumers Energy Company [Member]
Operating Revenue											2,340		2,354		2,556
Other Depreciation and amortization											130		122		118
Interest Expense											71		73		66
Income Tax Expense Benefit											77		67		56
Total Net Income Available to Common Stockholders											130		127		96
Plant And Property Gross	4,206					4,063					4,206		4,063		3,812
Total Assets	4,956	[2]				4,614	[2]				4,956	[2]	4,614	[2]	4,594	[2]
Capital Expenditures											261	[3]	235	[3]	270	[3]
Enterprises [Member]
Operating Revenue											204		238		216
Income (loss) from equity method investees											9	[1]	11	[1]	(2)	[1]
Other Depreciation and amortization											3		3		10
Interest Expense															5
Income Tax Expense Benefit											(24)		14		4
Total Net Income Available to Common Stockholders											32		36		(7)
Equity Method Investments	49	[1]				48	[1]				49	[1]	48	[1]	3	[1]
Plant And Property Gross	109					102					109		102		345
Total Assets	242	[2]				191	[2]				242	[2]	191	[2]	303	[2]
Capital Expenditures											5	[3]	4	[3]	7	[3]
Discontinued Operations [Member]
Total Net Income Available to Common Stockholders											2		(23)		20
Other [Member]
Operating Revenue											46		38		26
Other Depreciation and amortization											1		1		1
Interest Expense											152		156		139
Income Tax Expense Benefit											(52)		(44)		(52)
Total Net Income Available to Common Stockholders											(82)		(119)		(85)
Equity Method Investments	1	[1]				1	[1]				1	[1]	1	[1]	6	[1]
Plant And Property Gross	36					36					36		36		34
Total Assets	1,316	[2]				1,490	[2]				1,316	[2]	1,490	[2]	1,202	[2]
Capital Expenditures											1	[3]	2	[3]
Other [Member] | Consumers Energy Company [Member]
Interest Expense											2		2		1
Total Net Income Available to Common Stockholders											2		2		1
Plant And Property Gross	15					15					15		15		15
Total Assets	$ 768	[2]				$ 904	[2]				$ 768	[2]	$ 904	[2]	$ 871	[2]

[1] Consumers had no material equity method investments.

[2] Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.

[3] Amounts include purchase of capital lease additions. Amounts also include a portion of Consumers' capital expenditures for plant and equipment attributable to both the electric and gas utility businesses.