Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013
Debt Issuance [Member]
Debt Instrument [Line Items]
Debt issuance, principal	$ 1,000,000,000
Debt Issuance [Member] | CMS Energy [Member]
Debt Instrument [Line Items]
Debt issuance, principal	250,000,000
Debt Issuance [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt issuance, principal	750,000,000
Debt Issuance [Member] | Senior Notes 4.70% Due March 2043 [Member] | CMS Energy [Member]
Debt Instrument [Line Items]
Debt issuance, principal	250,000,000
Interest rate	4.70%
Debt issuance date	March 2013
Maturity date	March 2043
Debt Issuance [Member] | FMBs 3.95% Due May 2043 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt issuance, principal	425,000,000
Interest rate	3.95%
Debt issuance date	May 2013
Maturity date	May 2043
Debt Issuance [Member] | FMBs 3.375% Due August 2023 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt issuance, principal	325,000,000
Interest rate	3.375%
Debt issuance date	August 2013
Maturity date	August 2023
Debt Retirements [Member]
Debt Instrument [Line Items]
Debt retirement, principal	675,000,000
Debt Retirements [Member] | CMS Energy [Member]
Debt Instrument [Line Items]
Debt retirement, principal	250,000,000
Debt Retirements [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt retirement, principal	425,000,000
Debt Retirements [Member] | Senior Notes 2.750% Due May 2014 [Member] | CMS Energy [Member]
Debt Instrument [Line Items]
Debt retirement, principal	250,000,000
Interest rate	2.75%
Debt retirement date	September 2013
Maturity date	May 2014
Debt Retirements [Member] | FMB's 6% Due February 2014 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt retirement, principal	200,000,000
Interest rate	6.00%
Debt retirement date	June 2013
Maturity date	February 2014
Debt Retirements [Member] | FMB's 5% Due March 2015 [Member] | Consumers Energy Company [Member]
Debt Instrument [Line Items]
Debt retirement, principal	$ 225,000,000
Interest rate	5.00%
Debt retirement date	June 2013
Maturity date	March 2015