Financings and Capitalization (Major Long-Term Debt Transactions) (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
Debt Instrument [Line Items]
Principal balance	$ 930
Debt retirement, principal	480
CMS Energy Corporation
Debt Instrument [Line Items]
Principal balance	930
Debt retirement, principal	480
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	2019-12
CMS Energy Corporation \| Junior subordinated notes 5.875% due March 2079
Debt Instrument [Line Items]
Principal balance	$ 630
Interest Rate	5.875%
Debt issuance date	February 2019
Maturity Date	2079-03
CMS Energy Corporation \| Term loan facility due April 2019
Debt Instrument [Line Items]
Debt retirement, principal	$ 180
Debt retirement date	February 2019
Maturity Date	2019-04

Debt Instrument Issuance Date 2

No definition available.

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- Definition

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

No definition available.

+ Details

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- Definition

Maturity date of the debt instrument.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

+ Details

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