Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended																			1 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Oct. 31, 2010	Dec. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2012 NREPA [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Superfund Liability [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Manufactured Gas Plant [Member] Consumers Energy Company [Member] item	Dec. 31, 2012 MGP Sites [Member] Consumers Energy Company [Member]		Dec. 31, 2011 MGP Sites [Member] Consumers Energy Company [Member]		Dec. 31, 2012 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member]		Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]
Demand for payment by USEPA									$ 7
Cumulative environmental charge			227
Recorded liability			61											122
Accrual for environmental loss contingencies												4	2
Site contingency accrual inflation rate			1.00%											2.50%
Remaining undiscounted obligation amount			80											134
Undiscounted amount due in next fiscal year			12											11
Undiscounted amount due within two year			4											11
Undiscounted amount due within third year			4											20
Undiscounted amount due within fourth year			4											11
Undiscounted amount due within five year			4											10
Foreign government tax claim on sale			142
After tax income in discontinued operations recognized after expiration of tax indemnification	7	2	7	[1]	2	[2]	(23)	[3]
Remediation and other response activity costs, minimum												4	2
Remediation and other response activity costs. maximum												6	8
Discounted projected costs rate			4.34%											2.57%
Litigation settlement, gross																						120
Amount Paid to Transfer Ownership and Responsibility																			30	30
Number of former MGPs														23
Regulatory assets, noncurrent			$ 2,287		$ 2,466					$ 2,287	$ 2,466			$ 152	$ 152	[4]	$ 156	[4]		$ 85	[4]

[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.

[4] These regulatory assets represent expenditures for which the MPSC has provided, or Consumers expects, recovery without a return on investment.