Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
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	$ 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.

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