Financings and Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
Oct. 31, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Principal balance		$ 2,021
Debt retirement, principal		845
Consumers Energy Company
Debt Instrument [Line Items]
Principal balance		926
Debt retirement, principal		300
First mortgage bonds due February 2050 \| Consumers Energy Company
Debt Instrument [Line Items]
Principal balance		$ 300
Interest Rate		3.75%
Debt issuance date		May 2019
Maturity Date		February 2050
First Mortgage Bonds Due August 2050 \| Consumers Energy Company
Debt Instrument [Line Items]
Principal balance		$ 550
Interest Rate		3.10%
Debt issuance date		September 2019
Maturity Date		August 2050
Floating First Rate Mortgage Bonds Due September 2069 \| Consumers Energy Company
Debt Instrument [Line Items]
Principal balance		$ 76
Debt issuance date		September 2019
Maturity Date		September 2069
Effective interest rate		1.864%
First mortgage bonds due April 2020 \| Consumers Energy Company
Debt Instrument [Line Items]
Debt retirement, principal		$ 300
Interest Rate		5.65%
Debt retirement date		May 2019
Maturity Date		April 2020
CMS Energy Corporation
Debt Instrument [Line Items]
Principal balance		$ 1,095
Debt retirement, principal		545
CMS Energy Corporation \| Term loan facility due December 2019
Debt Instrument [Line Items]
Principal balance		300
Debt retirement, principal		$ 300
Debt issuance date		January 2019
Debt retirement date		February 2019
Maturity Date		December 2019
CMS Energy Corporation \| 5.875% Junior Subordinated Notes due 2079
Debt Instrument [Line Items]
Principal balance		$ 630
Interest Rate		5.875%
Debt issuance date		February 2019
Maturity Date		March 2079
CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Principal balance		$ 165
Debt retirement, principal		$ 65
Debt issuance date		June 2019
Debt retirement date		August 2019
Maturity Date		June 2020
Effective interest rate		2.552%
CMS Energy Corporation \| Term loan facility due April 2019
Debt Instrument [Line Items]
Debt retirement, principal		$ 180
Debt retirement date		February 2019
Maturity Date		April 2019
London Interbank Offered Rate (LIBOR) \| Floating First Rate Mortgage Bonds Due September 2069 \| Consumers Energy Company
Debt Instrument [Line Items]
Basis spread on variable rate		0.30%
Term Loan Facility Due June 2020 Tranche One \| CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Amount Borrowed		$ 5
Term Loan Facility Due June 2020 Tranche One \| London Interbank Offered Rate (LIBOR) \| CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Term Loan Facility Due June 2020 Tranche Two \| CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Amount Borrowed		$ 95
Term Loan Facility Due June 2020 Tranche Two \| London Interbank Offered Rate (LIBOR) \| CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Subsequent Event \| Term Loan Facility Due June 2020 Tranche One \| CMS Energy Corporation \| Term loan facility due June 2020
Debt Instrument [Line Items]
Debt retirement, principal	$ 5

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Date when the debt instrument was partially or fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

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Maturity date of the debt instrument.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

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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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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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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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