Plant, Property, and Equipment (Public Utilities, Allowance for Funds Used During Construction, Schedule of Composite Rate Table) (Details) (Consumers Energy Company [Member])	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consumers Energy Company [Member]
Public Utilities Allowance For Funds Used During Construction Composite Rate	7.30%	7.60%	7.60%

Disclosure of the composite rate of allowance for funds used during construction (AFUDC). The composite AFUDC rate is the average of the electric, gas, and common rates used during the period.

No definition available.

Name:	cms_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCompositeRate
Namespace Prefix:	cms_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration