Loss Contingency, Number of lawsuits

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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.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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Carrying amount of reserve for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs, which is expected to be paid within one year of the date of the statement of financial position.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Schedule I - Condensed Financial Information of Registrant (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) lawsuit	Dec. 31, 2019 USD ($)	Dec. 31, 2018	Jul. 31, 2018 USD ($)
CMS Energy
Condensed Financial Statements, Captions [Line Items]
Maximum potential obligation	$ 596
CMS Energy Note Payable
Condensed Financial Statements, Captions [Line Items]
Interest rate			4.10%
CMS Energy Note Payable \| Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Notes payable				$ 124
Class Action Lawsuits
Condensed Financial Statements, Captions [Line Items]
Number of lawsuits \| lawsuit	4
Individual Lawsuits
Condensed Financial Statements, Captions [Line Items]
Number of lawsuits \| lawsuit	1
Gas Index Price Reporting Litigation
Condensed Financial Statements, Captions [Line Items]
Estimated current litigation liability		$ 30