Financings and Capitalization (Summary of Long-Term Debt Outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Principal amounts outstanding	$ 7,654,000,000		$ 7,245,000,000
Current portion of long-term debt	(541,000,000)		(519,000,000)
Net unamortized discount	(12,000,000)		(16,000,000)
Total long-term debt	7,101,000,000		6,710,000,000
Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal amounts outstanding	4,625,000,000		4,341,000,000
Current portion of long-term debt	(43,000,000)		(41,000,000)
Net unamortized discount	(3,000,000)		(3,000,000)
Total long-term debt	4,579,000,000		4,297,000,000
CMS Energy [Member]
Debt Instrument [Line Items]
Principal amounts outstanding	2,377,000,000		2,377,000,000
Net unamortized discount	9,000,000		13,000,000
Total long-term debt	2,205,000,000		2,205,000,000
Term Loan Facility Due December 2016 [Member]
Debt Instrument [Line Items]
Maturity Date	2016
Principal amounts outstanding	180,000,000		180,000,000
Three-month LIBOR plus a spread, in basis points	1.75%
Interest rate at period end	1.92%
Securitization Bonds [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.76%	[1]
Maturity Date	2015
Principal amounts outstanding	92,000,000		133,000,000
Weighted-average Interest Rate (%)	5.76%		5.72%
Tax-Exempt Pollution Control Revenue Bonds [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Maturity Date	2018-2035
Principal amounts outstanding	103,000,000		103,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Principal amounts outstanding	2,197,000,000		2,197,000,000
Senior Notes [Member] | Senior Notes 2.75% Due May 2014 [Member]
Debt Instrument [Line Items]
Interest rate	2.75%	[2]
Maturity Date	2014
Principal amounts outstanding			250,000,000
Senior Notes [Member] | Senior Notes 6.875% Due December 2015 [Member]
Debt Instrument [Line Items]
Interest rate	6.875%
Maturity Date	2015
Principal amounts outstanding	125,000,000		125,000,000
Senior Notes [Member] | Senior Notes 4.25% Due September 2015 [Member]
Debt Instrument [Line Items]
Interest rate	4.25%
Maturity Date	2015
Principal amounts outstanding	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 6.55% Due July 2017 [Member]
Debt Instrument [Line Items]
Interest rate	6.55%
Maturity Date	2017
Principal amounts outstanding	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 5.05% Due February 2018 [Member]
Debt Instrument [Line Items]
Interest rate	5.05%
Maturity Date	2018
Principal amounts outstanding	250,000,000		250,000,000
Senior Notes [Member] | Senior Notes 8.75% Due June 2019 [Member]
Debt Instrument [Line Items]
Interest rate	8.75%
Maturity Date	2019
Principal amounts outstanding	300,000,000		300,000,000
Senior Notes [Member] | Senior Notes 6.25% Due February 2020 [Member]
Debt Instrument [Line Items]
Interest rate	6.25%
Maturity Date	2020
Principal amounts outstanding	300,000,000		300,000,000
Senior Notes [Member] | Senior Notes 5.05% Due March 2022 [Member]
Debt Instrument [Line Items]
Interest rate	5.05%
Maturity Date	2022
Principal amounts outstanding	300,000,000		300,000,000
Senior Notes [Member] | Senior Notes 5.5% Due June 2029 [Member]
Debt Instrument [Line Items]
Interest rate	5.50%	[3]
Maturity Date	2029
Principal amounts outstanding	172,000,000		172,000,000
Senior Notes [Member] | Senior Notes 4.7% Due March 2043 [Member]
Debt Instrument [Line Items]
Interest rate	4.70%
Maturity Date	2043
Principal amounts outstanding	250,000,000
Senior Notes [Member] | Senior Notes 6.875% Due March 2018 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	6.875%
Maturity Date	2018
Principal amounts outstanding	180,000,000		180,000,000
Other CMS Subsidiaries [Member]
Debt Instrument [Line Items]
Principal amounts outstanding	652,000,000		527,000,000
Other CMS Subsidiaries [Member] | EnerBank Certificates Of Deposit [Member]
Debt Instrument [Line Items]
Interest rate	1.095%	[4]
Maturity Date	2014-2021
Interest-bearing Domestic Deposit, Brokered	652,000,000		527,000,000
Weighted-average interest rate	1.09%		1.16%
Certificate of deposit face value	1,000
First Mortgage Bonds [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Principal amounts outstanding	4,250,000,000	[5]	3,925,000,000	[5]
Weighted-average Interest Rate (%)	4.90%		5.19%
First Mortgage Bonds [Member] | FMB's 6% Due February 2014 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	6.00%	[5],[6]
Maturity Date	2014	[5]
Principal amounts outstanding			200,000,000	[5]
First Mortgage Bonds [Member] | FMB's 5% Due March 2015 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.00%	[5],[6]
Maturity Date	2015	[5]
Principal amounts outstanding			225,000,000	[5]
First Mortgage Bonds [Member] | FMBs 2.6% Due October 2015 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	2.60%	[5]
Maturity Date	2015	[5]
Principal amounts outstanding	50,000,000	[5]	50,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.5% Due August 2016 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.50%	[5]
Maturity Date	2016	[5]
Principal amounts outstanding	350,000,000	[5]	350,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.15% Due February 2017 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.15%	[5]
Maturity Date	2017	[5]
Principal amounts outstanding	250,000,000	[5]	250,000,000	[5]
First Mortgage Bonds [Member] | FMBs 3.21% Due October 2017 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.21%	[5]
Maturity Date	2017	[5]
Principal amounts outstanding	100,000,000	[5]	100,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.65% Due September 2018 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.65%	[5]
Maturity Date	2018	[5]
Principal amounts outstanding	250,000,000	[5]	250,000,000	[5]
First Mortgage Bonds [Member] | FMBs 6.125% Due March 2019 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	6.125%	[5]
Maturity Date	2019	[5]
Principal amounts outstanding	350,000,000	[5]	350,000,000	[5]
First Mortgage Bonds [Member] | FMBs 6.7% Due September 2019 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	6.70%	[5]
Maturity Date	2019	[5]
Principal amounts outstanding	500,000,000	[5]	500,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.65% Due April 2020 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.65%	[5]
Maturity Date	2020	[5]
Principal amounts outstanding	300,000,000	[5]	300,000,000	[5]
First Mortgage Bonds [Member] | FMBs 3.77% Due October 2020 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.77%	[5]
Maturity Date	2020	[5]
Principal amounts outstanding	100,000,000	[5]	100,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.3% Due September 2022 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.30%	[5]
Maturity Date	2022	[5]
Principal amounts outstanding	250,000,000	[5]	250,000,000	[5]
First Mortgage Bonds [Member] | FMB's 2.85% Due May 2022 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	2.85%	[5]
Maturity Date	2022	[5]
Principal amounts outstanding	375,000,000	[5]	375,000,000	[5]
First Mortgage Bonds [Member] | FMBs 3.375% Due August 2023 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.375%	[5]
Maturity Date	2023	[5]
Principal amounts outstanding	325,000,000	[5]
First Mortgage Bonds [Member] | FMB's 3.19% Due 2024 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.19%	[5]
Maturity Date	2024	[5]
Principal amounts outstanding	52,000,000	[5]	52,000,000	[5]
First Mortgage Bonds [Member] | FMB's 3.39% Due 2027 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.39%	[5]
Maturity Date	2027	[5]
Principal amounts outstanding	35,000,000	[5]	35,000,000	[5]
First Mortgage Bonds [Member] | FMBs 5.8% Due September 2035 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	5.80%	[5]
Maturity Date	2035	[5]
Principal amounts outstanding	175,000,000	[5]	175,000,000	[5]
First Mortgage Bonds [Member] | FMBs 6.17% Due September 2040 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	6.17%	[5]
Maturity Date	2040	[5]
Principal amounts outstanding	50,000,000	[5]	50,000,000	[5]
First Mortgage Bonds [Member] | FMBs 4.97% Due October 2040 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	4.97%	[5]
Maturity Date	2040	[5]
Principal amounts outstanding	50,000,000	[5]	50,000,000	[5]
First Mortgage Bonds [Member] | FMB's 4.31% Due 2042 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	4.31%	[5]
Maturity Date	2042	[5]
Principal amounts outstanding	263,000,000	[5]	263,000,000	[5]
First Mortgage Bonds [Member] | FMBs 3.95% Due May 2043 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Interest rate	3.95%	[5]
Maturity Date	2043	[5]
Principal amounts outstanding	$ 425,000,000	[5]

[1] The weighted-average interest rate for Consumers’ Securitization bonds was 5.76 percent at December 31, 2013 and 5.72 percent at December 31, 2012.

[2] In September 2013, CMS Energy retired its 2.75 percent senior notes.

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

[4] The weighted-average interest rate for EnerBank’s certificates of deposit was 1.09 percent at December 31, 2013 and 1.16 percent at December 31, 2012. 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 4.90 percent at December 31, 2013 and 5.19 percent at December 31, 2012.

[6] In June 2013, Consumers retired its 6.00 percent and 5.00 percent FMBs.