Stock-Based Compensation (Schedule Of Share-Based Compensation, Stock Options, Activity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Stock-Based Compensation [Abstract]
Unrealized Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	$ 58

Unrealized tax benefit associated with any equity-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit cannot be recognized due to the use of tax loss carryforwards.

No definition available.

Name:	cms_UnrealizedAdjustmentsToAdditionalPaidInCapitalIncomeTaxBenefitFromShareBasedCompensation
Namespace Prefix:	cms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant