Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $)	3 Months Ended
Mar. 31, 2013
Senior Notes 2.75% Due May 2014 [Member] \| CMS Energy [Member]
Debt issuance, principal	$ 250,000,000
Interest rate	2.75%
Maturity date	May 2014
Debt Issuances [Member]
Debt issuance, principal	250,000,000
Debt Issuances [Member] \| Senior Notes 4.70% Due March 2043 [Member] \| CMS Energy [Member]
Debt issuance, principal	$ 250,000,000
Interest rate	4.70%
Debt issuance date	March 2013
Maturity date	March 2043

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant