Financial Instruments (Narrative) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Portion of long-term debt supported by third-party credit enhancements	$ 35
Consumers Energy Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Portion of long-term debt supported by third-party credit enhancements	$ 35

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration