Financings and Capitalization (Summary of Long-Term Debt Outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Principal Balance	$ 7,093,000,000		$ 7,206,000,000
Current portion of long-term debt	(1,033,000,000)		(726,000,000)
Net unamortized discount	(20,000,000)		(32,000,000)
Total long-term debt	6,040,000,000		6,448,000,000
Three-month LIBOR plus a spread, in basis points	2.00%
Consumers Energy Company [Member]
Total Consumers principal amounts outstanding	4,329,000,000		4,529,000,000
Current portion of long-term debt	(339,000,000)		(37,000,000)
Net unamortized discount	(3,000,000)		(4,000,000)
Total long-term debt	3,987,000,000		4,488,000,000
Trust Preferred Securities [Member]
Principal Balance	29,000,000
Senior Notes 6.875% Due March 2018 [Member]
Interest Rate	6.875%
Senior Notes 6.875% Due March 2018 [Member] | Consumers Energy Company [Member]
Maturity Date	2018
Principal Balance	180,000,000		180,000,000
Securitization Bonds [Member]
Interest Rate	5.652%	[1]
Securitization Bonds [Member] | Consumers Energy Company [Member]
Maturity Date - Earliest	2012
Maturity Date - Latest	2015
Principal Balance	171,000,000	[1]	208,000,000	[1]
Weighted-average Interest Rate (%)	5.652%		5.613%
Tax-Exempt Pollution Control Revenue Bonds [Member] | Consumers Energy Company [Member]
Maturity Date - Earliest	2018
Maturity Date - Latest	2035
Principal Balance	103,000,000		103,000,000
Interest rate at period end			0.132%
Senior Notes [Member]
Principal Balance	2,273,000,000		2,285,000,000
Senior Notes [Member] | Senior Notes 8.5% Due April 2011 [Member]
Interest Rate	8.50%
Maturity Date	2011
Principal Balance			146,000,000
Senior Notes [Member] | Senior Notes 6.3% Due February 2012 [Member]
Interest Rate	6.30%
Maturity Date	2012
Principal Balance			50,000,000
Senior Notes [Member] | Senior Notes Variable Rate Due January 2013 [Member]
Maturity Date	2013
Principal Balance	150,000,000		150,000,000
Bear interest at three-month LIBOR plus a spread, in basis points	three-month LIBOR
Three-month LIBOR plus a spread, in basis points	0.95%
Interest rate at period end	1.353%		1.239%
Senior Notes [Member] | Senior Notes 2.75% Due May 2014 [Member]
Interest Rate	2.75%
Maturity Date	2014
Principal Balance	250,000,000
Senior Notes [Member] | Senior Notes 6.875% Due December 2015 [Member]
Interest Rate	6.875%
Maturity Date	2015
Principal Balance	125,000,000		125,000,000
Senior Notes [Member] | Senior Notes 4.25% Due September 2015 [Member]
Interest Rate	4.25%
Maturity Date	2015
Principal Balance	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 6.55% Due July 2017 [Member]
Interest Rate	6.55%
Maturity Date	2017
Principal Balance	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 5.05% Due February 2018 [Member]
Interest Rate	5.05%
Maturity Date	2018
Principal Balance	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 8.75% Due June 2019 [Member]
Interest Rate	8.75%
Maturity Date	2019
Principal Balance	300,000,000		300,000,000
Senior Notes [Member] | Senior Notes 6.25% Due February 2020 [Member]
Interest Rate	6.25%
Maturity Date	2020
Principal Balance	300,000,000		300,000,000
Senior Notes [Member] | Senior Notes 3.375% Due December 2023 [Member]
Interest Rate	3.375%	[2]
Maturity Date	2023
Principal Balance			4,000,000
Senior Notes [Member] | Senior Notes 2.875% Due December 2024 [Member]
Interest Rate	2.875%	[2]
Maturity Date	2024
Principal Balance	226,000,000		288,000,000
Senior Notes [Member] | Senior Notes 5.5% Due June 2029 [Member]
Interest Rate	5.50%	[2]
Maturity Date	2029
Principal Balance	172,000,000		172,000,000
Other CMS Subsidiaries [Member]
Principal Balance	491,000,000		392,000,000
Other CMS Subsidiaries [Member] | Trust Preferred Securities [Member]
Interest Rate	7.75%
Maturity Date	2027
Principal Balance	29,000,000		29,000,000
Other CMS Subsidiaries [Member] | EnerBank certificates of deposit [Member]
Weighted-average interest rate	1.328%	[3]	1.707%
Maturity Date - Earliest	2012
Maturity Date - Latest	2018
Interest-bearing Domestic Deposit, Brokered	462,000,000		363,000,000
Certificate of deposit face value	1,000
First Mortgage Bonds [Member] | Consumers Energy Company [Member]
Total Consumers principal amounts outstanding	3,875,000,000		3,875,000,000
Weighted-average Interest Rate (%)	5.50%		5.50%
First Mortgage Bonds [Member] | FMBs 5 percent Due February 2012 [Member]
Interest Rate	5.00%	[4]
First Mortgage Bonds [Member] | FMBs 5 percent Due February 2012 [Member] | Consumers Energy Company [Member]
Maturity Date	2012	[4]
Principal Balance	300,000,000	[4]	300,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.375 percent Due April 2013 [Member]
Interest Rate	5.375%	[4]
First Mortgage Bonds [Member] | FMBs 5.375 percent Due April 2013 [Member] | Consumers Energy Company [Member]
Maturity Date	2013	[4]
Principal Balance	375,000,000	[4]	375,000,000	[4]
First Mortgage Bonds [Member] | FMBs 6 percent Due February 2014 [Member]
Interest Rate	6.00%	[4]
First Mortgage Bonds [Member] | FMBs 6 percent Due February 2014 [Member] | Consumers Energy Company [Member]
Maturity Date	2014	[4]
Principal Balance	200,000,000	[4]	200,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5 percent Due March 2015 [Member]
Interest Rate	5.00%	[4]
First Mortgage Bonds [Member] | FMBs 5 percent Due March 2015 [Member] | Consumers Energy Company [Member]
Maturity Date	2015	[4]
Principal Balance	225,000,000	[4]	225,000,000	[4]
First Mortgage Bonds [Member] | FMBs 2.6 percent Due October 2015 [Member]
Interest Rate	2.60%	[4]
First Mortgage Bonds [Member] | FMBs 2.6 percent Due October 2015 [Member] | Consumers Energy Company [Member]
Maturity Date	2015	[4]
Principal Balance	50,000,000	[4]	50,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.5 percent Due August 2016 [Member]
Interest Rate	5.50%	[4]
First Mortgage Bonds [Member] | FMBs 5.5 percent Due August 2016 [Member] | Consumers Energy Company [Member]
Maturity Date	2016	[4]
Principal Balance	350,000,000	[4]	350,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.15 percent Due February 2017 [Member]
Interest Rate	5.15%	[4]
First Mortgage Bonds [Member] | FMBs 5.15 percent Due February 2017 [Member] | Consumers Energy Company [Member]
Maturity Date	2017	[4]
Principal Balance	250,000,000	[4]	250,000,000	[4]
First Mortgage Bonds [Member] | FMBs 3.21 percent Due October 2017 [Member]
Interest Rate	3.21%	[4]
First Mortgage Bonds [Member] | FMBs 3.21 percent Due October 2017 [Member] | Consumers Energy Company [Member]
Maturity Date	2017	[4]
Principal Balance	100,000,000	[4]	100,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.65 percent Due September 2018 [Member]
Interest Rate	5.65%	[4]
First Mortgage Bonds [Member] | FMBs 5.65 percent Due September 2018 [Member] | Consumers Energy Company [Member]
Maturity Date	2018	[4]
Principal Balance	250,000,000	[4]	250,000,000	[4]
First Mortgage Bonds [Member] | FMBs 6.125 percent Due March 2019 [Member]
Interest Rate	6.125%	[4]
First Mortgage Bonds [Member] | FMBs 6.125 percent Due March 2019 [Member] | Consumers Energy Company [Member]
Maturity Date	2019	[4]
Principal Balance	350,000,000	[4]	350,000,000	[4]
First Mortgage Bonds [Member] | FMBs 6.7 percent Due September 2019 [Member]
Interest Rate	6.70%	[4]
First Mortgage Bonds [Member] | FMBs 6.7 percent Due September 2019 [Member] | Consumers Energy Company [Member]
Maturity Date	2019	[4]
Principal Balance	500,000,000	[4]	500,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.65 percent Due April 2020 [Member]
Interest Rate	5.65%	[4]
First Mortgage Bonds [Member] | FMBs 5.65 percent Due April 2020 [Member] | Consumers Energy Company [Member]
Maturity Date	2020	[4]
Principal Balance	300,000,000	[4]	300,000,000	[4]
First Mortgage Bonds [Member] | FMBs 3.77 percent Due October 2020 [Member]
Interest Rate	3.77%	[4]
First Mortgage Bonds [Member] | FMBs 3.77 percent Due October 2020 [Member] | Consumers Energy Company [Member]
Maturity Date	2020	[4]
Principal Balance	100,000,000	[4]	100,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.3 percent Due September 2022 [Member]
Interest Rate	5.30%	[4]
First Mortgage Bonds [Member] | FMBs 5.3 percent Due September 2022 [Member] | Consumers Energy Company [Member]
Maturity Date	2022	[4]
Principal Balance	250,000,000	[4]	250,000,000	[4]
First Mortgage Bonds [Member] | FMBs 5.8 percent Due September 2035 [Member]
Interest Rate	5.80%	[4]
First Mortgage Bonds [Member] | FMBs 5.8 percent Due September 2035 [Member] | Consumers Energy Company [Member]
Maturity Date	2035	[4]
Principal Balance	175,000,000	[4]	175,000,000	[4]
First Mortgage Bonds [Member] | FMBs 6.17 percent Due September 2040 [Member]
Interest Rate	6.17%	[4]
First Mortgage Bonds [Member] | FMBs 6.17 percent Due September 2040 [Member] | Consumers Energy Company [Member]
Maturity Date	2040	[4]
Principal Balance	50,000,000	[4]	50,000,000	[4]
First Mortgage Bonds [Member] | FMBs 4.97 percent Due October 2040 [Member]
Interest Rate	4.97%	[4]
First Mortgage Bonds [Member] | FMBs 4.97 percent Due October 2040 [Member] | Consumers Energy Company [Member]
Maturity Date	2040	[4]
Principal Balance	50,000,000	[4]	50,000,000	[4]
Nuclear Fuel Disposal Liability [Member]
Interest rate at period end			0.132%	[4]
Nuclear Fuel Disposal Liability [Member] | Consumers Energy Company [Member]
Principal Balance			$ 163,000,000	[4]

[1] The weighted-average interest rate for Consumers' Securitization bonds was 5.652 percent at December 31, 2011 and 5.613 percent at December 31, 2010.

[2] CMS Energy's contingently convertible notes. See the "Contingently Convertible Securities" section in this Note for further discussion of the conversion features.

[3] The weighted-average interest rate for EnerBank's certificates of deposit was 1.328 percent at December 31, 2011 and 1.707 percent at December 31, 2010. EnerBank's primary deposit product consists of brokered certificates of deposit with varying maturities. EnerBank sells these deposits through investment brokers in large pools, with each certificate within the pool having a face value of $1,000. They cannot be withdrawn until maturity, except in the case of death or incompetence of the holder.

[4] The weighted-average interest rate for Consumers' FMBs was 5.5 percent at December 31, 2011 and 2010.