Financings and Capitalization (Forward Stock Contracts) (Details) - $ / shares	Feb. 21, 2019	Nov. 20, 2018
Forward Contracts Entered Into November 2018 and Maturing March 2021
Debt and Equity Securities, FV-NI [Line Items]
Number of Shares		777,899
Initial forward price (in dollars per share)		$ 50.91
Forward Contracts Entered into February 2019 and Maturing March 2021
Debt and Equity Securities, FV-NI [Line Items]
Number of Shares	2,083,340
Initial forward price (in dollars per share)	$ 52.27

The per share price of the Company's stock at which the contract holder of the freestanding contract has the right to purchase or sell the Company's stock at a future date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879

+ Details

Name:	us-gaap_ForwardContractIndexedToIssuersEquityForwardRate
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum number of shares that could be issued to net share settle a contract, if applicable. If a contract does not have a fixed or determinable maximum number of shares that may be required to be issued, disclose the fact that a potentially infinite number of shares could be issued to settle the contract.

+ References

+ Details

Name:	us-gaap_ForwardContractIndexedToIssuersEquityShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis=cms_ForwardContractsEnteredIntoNovember202018AndMaturingMarch312021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis=cms_ForwardContractsEnteredIntoFebruary212019AndMaturingMarch312021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: