Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financial Instruments [Line Items]
Portion of long-term debt supported by third-party credit enhancements	$ 103	$ 103
Consumers Energy Company [Member]
Financial Instruments [Line Items]
Portion of long-term debt supported by third-party credit enhancements	$ 103	$ 103

Disclosure of the amount of the entity's issued liability supported by a third-party credit enhancement.

No definition available.

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