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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
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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

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- Definition Number of new stock issued during the period. + References 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 -Article 5 + Details
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