Asset Sales, Discontinued Operations, and Impairment Charges (Discontinued Operations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended													12 Months Ended
	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2010 CMS Energy Corporation [Member]	Dec. 31, 2010 Exeter [Member]	Dec. 31, 2009 Exeter [Member]	Dec. 31, 2010 2003 Asset Sale [Member]	Dec. 31, 2010 2007 Asset Sale [Member]	Dec. 31, 2009 2007 Asset Sale [Member]	Dec. 31, 2007 2007 Asset Sale [Member]	Dec. 31, 2010 2002 Asset Sale [Member]
Revenues from Discontinued Operations							$ 10		$ 7
Income (Loss) From Discontinued Operations, Before Income Tax, Total					2		(21)		33
Tax Effect of Discontinued Operations							2		13
Income (Loss) From Discontinued Operations, Net of Tax, Total	2	(6)	(16)	(1)	2	[1]	(23)	[2]	20	[3]	(10)
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, before Income Tax												2	11
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax												1	7
Discontinued Operation, Amount of Adjustment to Prior Period Gain (Loss) on Disposal, Net of Tax					3				(2)					(10)	(3)	28		(3)
Discontinued Operation, Provision for Loss (Gain) on Disposal, before Income Tax												6
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax												4
Discontinued Operation, Amount of Adjustment to Prior Period Gain (Loss) on Disposal, before Income Tax									(3)						(5)	45		(5)
Gain on asset sales, net					0		6		13							5
Interest Paid, Discontinued Operations					1		1		1
Loss Contingency Accrual, at Carrying Value																	50
Cash Held-for-sale, Current												1
Receivables Held-for-sale, Net Amount												1
Assets Held-for-sale, Property, Plant and Equipment												3
Assets Held-for-sale, Other, Noncurrent												1
Assets of Disposal Group, Including Discontinued Operation, Total												6
Liabilities of Disposal Group, Including Discontinued Operation, Current		1					1					1
Liabilities of Disposal Group, Including Discontinued Operation												$ 1

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

[2] 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. Also includes disposal-related losses of $10 million in additional tax expense resulting from an IRS audit adjustment related to a 2003 asset sale, a $6 million ($4 million net of tax) loss for the write down of CMS Energy's investment in Exeter, a $5 million ($3 million net of tax) loss for the increase in a liability for a 2007 asset sale, and a $5 million ($3 million net of tax) loss on the settlement of a 2002 asset sale indemnity.

[3] Includes an operating loss of $11 million ($7 million net of tax) at Exeter and a loss of $3 million ($2 million net of tax) related to a litigation settlement at CMS Viron. Also includes a gain for the expiration of an indemnity obligation related to a 2007 asset sale. CMS Energy provided an indemnity to TAQA in connection with the sale of its ownership interests in businesses in the Middle East, Africa, and India, and recorded a $50 million provision for the contingent liability. This indemnity expired in 2009 and CMS Energy eliminated the liability from its consolidated balance sheets, recognizing a $45 million benefit ($28 million net of tax) to income (loss) from discontinued operations and a $5 million benefit to gain on asset sales, net.