Financings And Capitalization (Issuance Of Common Stock) (Details) (CMS Energy [Member], USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	30 Months Ended
Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2011	Sep. 30, 2013
CMS Energy [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Shares Issued	735,873	650,235	762,925	2,149,033
Average Price Per Share	$ 27.18	$ 23.07	$ 19.66	$ 23.27
Proceeds	$ 20	$ 15	$ 15	$ 50

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration