Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $)	1 Months Ended								9 Months Ended																								9 Months Ended
	Jul. 31, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 3.19% Due 2024 [Member] Consumers Energy Company [Member]	Jul. 31, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 3.39% Due 2027 [Member] Consumers Energy Company [Member]	Jul. 31, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 4.31% Due 2042 [Member] Consumers Energy Company [Member]	Aug. 31, 2012 Tax Exempt Bonds Variable [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Short Term Credit Agreement Due March 2013 [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Issuances [Member]	Sep. 30, 2012 Debt Issuances [Member] CMS Energy Corporation [Member]	Sep. 30, 2012 Debt Issuances [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Issuances [Member] First Mortgage Bonds 2.85% Due May 2022 [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Issuances [Member] Senior Notes 5.05% Due March 2022 [Member] CMS Energy Corporation [Member]	Sep. 30, 2012 Debt Issuances [Member] Term Loan Facility Due December 2016 [Member] CMS Energy Corporation [Member]		Sep. 30, 2012 Debt Issuances [Member] Term Loan Facility Due March 2013 [Member] Consumers Energy Company [Member]		Sep. 30, 2012 Debt Issuances [Member] Tax Exempt Bonds Variable Due April 2018 [Member] Consumers Energy Company [Member]		Sep. 30, 2012 Debt Issuances [Member] Tax Exempt Bonds Variable Due April 2035 [Member] Consumers Energy Company [Member]		Sep. 30, 2012 Debt Retirements [Member]	Sep. 30, 2012 Debt Retirements [Member] CMS Energy Corporation [Member]	Sep. 30, 2012 Debt Retirements [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Retirements [Member] First Mortgage Bonds 5% Due February 2012 [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Retirements [Member] First Mortgage Bonds 5.375% Due April 2013 [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Debt Retirements [Member] Senior Notes 2.875% Due December 2024 [Member] CMS Energy Corporation [Member]		Sep. 30, 2012 Debt Retirements [Member] Tax Exempt Bonds Variable Due April 2018 [Member] Consumers Energy Company [Member]		Sep. 30, 2012 Debt Retirements [Member] Tax Exempt Bonds Variable Due April 2035 [Member] Consumers Energy Company [Member]		Sep. 30, 2012 Debt Retirements [Member] Senior Notes Variable Rate Due January 2013 [Member] CMS Energy Corporation [Member]	Sep. 30, 2012 Debt Retirements [Member] Trust Preferred Securities [Member]	Sep. 30, 2011 Debt Retirements [Member] Trust Preferred Securities [Member]	Sep. 30, 2012 Debt Retirements [Member] Trust Preferred Securities [Member] CMS Energy Corporation [Member]
Debt issuance, principal	$ 52,000,000	$ 35,000,000	$ 263,000,000			$ 1,308,000,000	$ 480,000,000	$ 828,000,000	$ 375,000,000	$ 300,000,000	$ 180,000,000	[1],[2]	$ 350,000,000	[3]	$ 68,000,000	[4]	$ 35,000,000	[4]
Debt retirement, principal																			1,183,000,000	405,000,000	778,000,000	300,000,000	375,000,000	226,000,000	[5]	68,000,000	[4]	35,000,000	[4]	150,000,000			29,000,000
Interest rate	3.19%	3.39%	4.31%						2.85%	5.05%												5.00%	5.38%	2.88%	[5]								7.75%
Interest rate (variable)											variable	[1],[2]	variable	[3]	variable	[4]	variable	[4]								variable	[4]	variable	[4]	variable
Debt issuance date									May 2012	March 2012	February 2012 and July 2012	[1],[2]	June 2012	[3]	August 2012	[4]	August 2012	[4]
Debt retirement date																						February 2012	May 2012	January 2012 and April 2012	[5]	August 2012	[4]	August 2012	[4]	July 2012	February 2012	February 2012	February 2012
Maturity date	2024	2027	2042						May 2022	March 2022	December 2016	[1],[2]	March 2013	[3]	April 2018	[4]	April 2035	[4]				February 2012	April 2013	December 2024	[5]	April 2018	[4]	April 2035	[4]	January 2013			July 2027
Debt retirement face amount				103,000,000
Interest rate terms											LIBOR plus 2.5 percent		LIBOR plus 0.8 percent
LIBOR plus											2.50%		0.80%
Amount of Facility					$ 375,000,000

[1] Principal Issue/Retirement(In Millions) Interest Rate DateMaturity Date Debt IssuancesCMS EnergySenior notes$ 300 5.05%March 2012March 2022 Term loan facility1,2 180variable February 2012 and July 2012December 2016 CMS Energy Total 480ConsumersFMB 375 2.85%May 2012May 2022 Term loan facility3 350variable June 2012March 2013 Tax-exempt bonds4 68variable August 2012April 2018 Tax-exempt bonds4 35variable August 2012April 2035 Consumers Total 828Total$ 1,308Debt RetirementsCMS EnergyContingently convertible senior notes5$ 226 2.88%January 2012 and April 2012December 2024 Trust Preferred Securities 29 7.75%February 2012July 2027 Senior notes 150variable July 2012January 2013 CMS Energy Total 405ConsumersFMB 300 5.00%February 2012February 2012 FMB 375 5.38%May 2012April 2013 Tax-exempt bonds4 68variable August 2012April 2018 Tax-exempt bonds4 35variable August 2012April 2035 Consumers Total 778Total$ 1,183Outstanding borrowings bear interest at an annual interest rate of LIBOR plus 2.5 percent.

[2] CMS Energy used these proceeds to retire the 7.75 percent Trust Preferred Securities and floating-rate senior notes due January 2013.

[3] In June 2012, Consumers entered into a short-term credit agreement permitting Consumers to borrow up to $375 million. Outstanding borrowings bear interest at an annual interest rate of LIBOR plus 0.8 percent.

[4] In August 2012, Consumers utilized the Michigan Strategic Fund for the issuance of $68 million and $35 million of tax-exempt Michigan Strategic Fund revenue bonds. The bonds, which are backed by letters of credit and collateralized by Consumers’ FMBs, are subject to optional tender by the holders that would result in remarketing. Consumers used the proceeds to redeem $103 million of tax-exempt bonds in August 2012.

[5] CMS Energy’s contingently convertible notes. See the “Contingently Convertible Securities” section in this Note for further discussion of the conversions.