Financings and Capitalization (Summary of Long-Term Debt Outstanding) (Details) (USD $)							12 Months Ended		12 Months Ended			12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended				12 Months Ended			12 Months Ended				12 Months Ended			12 Months Ended							12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended												12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2012 CMS Energy [Member]	Dec. 31, 2011 CMS Energy [Member]	Dec. 31, 2012 Term Loan Facility Due December 2016 [Member]	Feb. 28, 2013 Term Loan Facility Due December 2016 [Member]	Dec. 31, 2012 Securitization Bonds [Member] Consumers Energy Company [Member]		Dec. 31, 2011 Securitization Bonds [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Tax-Exempt Pollution Control Revenue Bonds [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Tax-Exempt Pollution Control Revenue Bonds [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Senior Notes [Member]	Dec. 31, 2011 Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes Variable Rate Due January 2013 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes Variable Rate Due January 2013 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 2.75% Due May 2014 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 2.75% Due May 2014 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 6.875% Due December 2015 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 6.875% Due December 2015 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 4.25% Due September 2015 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 4.25% Due September 2015 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 6.55% Due July 2017 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 6.55% Due July 2017 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 5.05% Due February 2018 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 5.05% Due February 2018 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 8.75% Due June 2019 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 8.75% Due June 2019 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 6.25% Due February 2020 [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 6.25% Due February 2020 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 5.05% Due March 2022 [Member]	Dec. 31, 2012 Senior Notes [Member] 2.875% Convertible Senior Notes Due 2024 [Member]		Dec. 31, 2011 Senior Notes [Member] 2.875% Convertible Senior Notes Due 2024 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 5.5% Due June 2029 [Member]		Dec. 31, 2011 Senior Notes [Member] Senior Notes 5.5% Due June 2029 [Member]	Dec. 31, 2012 Senior Notes [Member] Senior Notes 6.875% Due March 2018 [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Senior Notes [Member] Senior Notes 6.875% Due March 2018 [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Other CMS Subsidiaries [Member]	Dec. 31, 2011 Other CMS Subsidiaries [Member]	Dec. 31, 2012 Other CMS Subsidiaries [Member] Trust Preferred Securities [Member]		Dec. 31, 2011 Other CMS Subsidiaries [Member] Trust Preferred Securities [Member]	Dec. 31, 2012 Other CMS Subsidiaries [Member] EnerBank certificates of deposit [Member]		Dec. 31, 2011 Other CMS Subsidiaries [Member] EnerBank certificates of deposit [Member]	Dec. 31, 2012 First Mortgage Bonds [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5% Due February 2012 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5% Due February 2012 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.375% Due April 2013 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.375% Due April 2013 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 6% Due February 2014 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 6% Due February 2014 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5% Due March 2015 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5% Due March 2015 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 2.6% Due October 2015 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 2.6% Due October 2015 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.5% Due August 2016 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.5% Due August 2016 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.15% Due February 2017 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.15% Due February 2017 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 3.21% Due October 2017 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 3.21% Due October 2017 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.65% Due September 2018 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.65% Due September 2018 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 6.125% Due March 2019 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 6.125% Due March 2019 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 6.7% Due September 2019 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 6.7% Due September 2019 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.65% Due April 2020 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.65% Due April 2020 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 3.77% Due October 2020 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 3.77% Due October 2020 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.3% Due September 2022 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.3% Due September 2022 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] First Mortgage Bonds 2.85% Due May 2022 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] First Mortgage Bonds 3.19% Due 2024 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] First Mortgage Bonds 3.39% Due 2027 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] First Mortgage Bonds 4.31% Due 2042 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 5.8% Due September 2035 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 5.8% Due September 2035 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 6.17% Due September 2040 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 6.17% Due September 2040 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] FMBs 4.97% Due October 2040 [Member] Consumers Energy Company [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] FMBs 4.97% Due October 2040 [Member] Consumers Energy Company [Member]		Dec. 31, 2012 Debt Issuances [Member]	Dec. 31, 2012 Debt Issuances [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Debt Issuances [Member] CMS Energy [Member]	Feb. 28, 2013 Debt Issuances [Member] Term Loan Facility Due December 2016 [Member] CMS Energy [Member]	Dec. 31, 2012 Debt Issuances [Member] Term Loan Facility Due December 2016 [Member] CMS Energy [Member]		Dec. 31, 2012 Debt Retirements [Member] Trust Preferred Securities [Member] CMS Energy [Member]	Dec. 31, 2012 Debt Retirements [Member] 2.875% Convertible Senior Notes Due 2024 [Member] CMS Energy [Member]
Interest rate									5.718%	[1]								2.75%		6.875%		4.25%		6.55%		5.05%		8.75%		6.25%		5.05%	2.875%	[2]		5.50%	[2]		6.875%				7.75%	[3]		1.164%	[4]						5.00%	[5]			5.375%	[5],[6]			6.00%	[5]			5.00%	[5]			2.60%	[5]			5.50%	[5]			5.15%	[5]			3.21%	[5]			5.65%	[5]			6.125%	[5]			6.70%	[5]			5.65%	[5]			3.77%	[5]			5.30%	[5]			2.85%	[5]	3.19%	[5]	3.39%	[5]	4.31%	[5]	5.80%	[5]			6.17%	[5]			4.97%	[5]									7.75%	2.875%	[7]
Weighted-average interest rate																																														1.16%		1.33%
Maturity Date							2016		2013-2015			2018-2035				2013		2014		2015		2015		2017		2018		2019		2020		2022	2024			2029			2018				2027			2013-2020							2012	[5]			2013	[5]			2014	[5]			2015	[5]			2015	[5]			2016	[5]			2017	[5]			2017	[5]			2018	[5]			2019	[5]			2019	[5]			2020	[5]			2020	[5]			2022	[5]			2022	[5]	2024	[5]	2027	[5]	2042	[5]	2035	[5]			2040	[5]			2040	[5]
Principal Balance					$ 2,377,000,000	$ 2,273,000,000	$ 180,000,000		$ 133,000,000		$ 171,000,000	$ 103,000,000	$ 103,000,000	$ 2,197,000,000	$ 2,273,000,000		$ 150,000,000	$ 250,000,000	$ 250,000,000	$ 125,000,000	$ 125,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 300,000,000	$ 300,000,000	$ 300,000,000	$ 300,000,000	$ 300,000,000			$ 226,000,000	$ 172,000,000		$ 172,000,000	$ 180,000,000	$ 180,000,000	$ 527,000,000	$ 491,000,000			$ 29,000,000				$ 3,925,000,000	[5]	$ 3,875,000,000	[5]			$ 300,000,000	[5]			$ 375,000,000	[5]	$ 200,000,000	[5]	$ 200,000,000	[5]	$ 225,000,000	[5]	$ 225,000,000	[5]	$ 50,000,000	[5]	$ 50,000,000	[5]	$ 350,000,000	[5]	$ 350,000,000	[5]	$ 250,000,000	[5]	$ 250,000,000	[5]	$ 100,000,000	[5]	$ 100,000,000	[5]	$ 250,000,000	[5]	$ 250,000,000	[5]	$ 350,000,000	[5]	$ 350,000,000	[5]	$ 500,000,000	[5]	$ 500,000,000	[5]	$ 300,000,000	[5]	$ 300,000,000	[5]	$ 100,000,000	[5]	$ 100,000,000	[5]	$ 250,000,000	[5]	$ 250,000,000	[5]	$ 375,000,000	[5]	$ 52,000,000	[5]	$ 35,000,000	[5]	$ 263,000,000	[5]	$ 175,000,000	[5]	$ 175,000,000	[5]	$ 50,000,000	[5]	$ 50,000,000	[5]	$ 50,000,000	[5]	$ 50,000,000	[5]	$ 1,658,000,000	$ 1,178,000,000	$ 480,000,000		$ 180,000,000	[8]
Interest-bearing Domestic Deposit, Brokered																																														527,000,000		462,000,000
Principal amounts outstanding	7,245,000,000	7,093,000,000	4,341,000,000	4,329,000,000
Current portion of long-term debt	(519,000,000)	(1,033,000,000)	(41,000,000)	(339,000,000)
Net unamortized discount	(16,000,000)	(20,000,000)	(3,000,000)	(3,000,000)	13,000,000	17,000,000
Total long-term debt	6,710,000,000	6,040,000,000	4,297,000,000	3,987,000,000	2,205,000,000	1,875,000,000
Bear interest at three-month LIBOR plus a spread, in basis points																three-month LIBOR
Three-month LIBOR plus a spread, in basis points							2.50%	2.00%								0.95%																																																																																																																				2.00%	2.50%
Interest rate at period end							2.71%										1.35%																																																																																																																				2.71%
Certificate of deposit face value																																														$ (1,000)
Weighted-average Interest Rate (%)									5.72%		5.65%																																						5.19%		5.52%

[1] The weighted-average interest rate for Consumers’ Securitization bonds was 5.72 percent at December 31, 2012 and 5.65 percent at December 31, 2011.

[2] CMS Energy’s contingently convertible notes. CMS Energy’s 2.875 percent senior notes were converted in January and April 2012. See the “Contingently Convertible Securities” section in this Note for further discussion of the conversion features.

[3] In February 2012, CMS Energy retired the 7.75 percent Trust Preferred Securities.

[4] The weighted-average interest rate for EnerBank’s certificates of deposit was 1.16 percent at December 31, 2012 and 1.33 percent at December 31, 2011. EnerBank’s primary deposit product consists of brokered certificates of deposit with varying maturities and having a face value of $1,000.

[5] The weighted-average interest rate for Consumers’ FMBs was 5.19 percent at December 31, 2012 and 5.52 percent at December 31, 2011.

[6] In May 2012, Consumers retired its 5.375 percent FMBs.

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

[8] Outstanding borrowings bear interest at an annual interest rate of LIBOR plus 2.50 percent (2.71 percent at December 31, 2012). CMS Energy used these proceeds to retire the 7.75 percent Trust Preferred Securities and floating-rate senior notes due January 2013. In February 2013, the term loan facility was amended, reducing the annual interest rate to LIBOR plus 2.00 percent.