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Carrying amount as of the balance sheet date of obligations due all related parties.

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Amount of investment in equity method investee and investment in and advance to affiliate.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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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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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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Related Party Transactions - Consumers (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2019	Jul. 31, 2018
Related Party Transaction [Line Items]
Purchased power – related parties	$ 81,000,000	$ 86,000,000	$ 86,000,000
Consumers Energy Company
Related Party Transaction [Line Items]
Purchased power – related parties	83,000,000	90,000,000	$ 88,000,000
Due to related parties	20,000,000	27,000,000
Accounts receivable - related parties	13,000,000	2,000,000
Investments	1,000,000	$ 21,000,000
Consumers Energy Company \| Credit Agreement
Related Party Transaction [Line Items]
Amount outstanding	$ 0
Subsequent Event \| Consumers Energy Company \| Credit Agreement
Related Party Transaction [Line Items]
Maximum borrowing capacity				$ 300,000,000
CMS Energy Note Payable
Related Party Transaction [Line Items]
Notes payable					$ 146,000,000