Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013
Senior Notes 2.75% Due May 2014 [Member] | CMS Energy [Member]
Debt issuance, principal	$ 250,000,000
Interest rate	2.75%
Maturity date	May 2014
Debt Issuance [Member]
Debt issuance, principal	675,000,000
Debt Issuance [Member] | CMS Energy [Member]
Debt issuance, principal	250,000,000
Debt Issuance [Member] | Consumers Energy Company [Member]
Debt issuance, principal	425,000,000
Debt Issuance [Member] | Senior Notes 4.70% Due March 2043 [Member] | CMS Energy [Member]
Debt issuance, principal	250,000,000	[1]
Interest rate	4.70%	[1]
Debt issuance date	March 2013	[1]
Maturity date	March 2043	[1]
Debt Issuance [Member] | First Mortgage Bonds 3.95% Due May 2043 [Member] | Consumers Energy Company [Member]
Debt issuance, principal	425,000,000
Interest rate	3.95%
Debt issuance date	May 2013
Maturity date	May 2043
Debt Retirements [Member]
Debt issuance, principal	425,000,000
Debt Retirements [Member] | Consumers Energy Company [Member]
Debt issuance, principal	425,000,000
Debt Retirements [Member] | First Mortgage Bonds 6% Due February 2014 [Member] | Consumers Energy Company [Member]
Debt issuance, principal	200,000,000
Interest rate	6.00%
Debt issuance date	June 2013
Maturity date	February 2014
Debt Retirements [Member] | First Mortgage Bonds 5% Due March 2015 [Member] | Consumers Energy Company [Member]
Debt issuance, principal	$ 225,000,000
Interest rate	5.00%
Debt issuance date	June 2013
Maturity date	March 2015

[1] CMS Energy plans to use these proceeds to retire all $250 million of CMS Energy’s 2.75 percent senior notes due May 2014.