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Financial Instruments (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jan. 31, 2015 | Jun. 30, 2015 | Dec. 31, 2014
Financial Instruments [Line Items] |  |  |
Portion of long-term debt supported by third-party credit enhancements |  | $ 103 | $ 103
Consumers Energy Company [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Portion of long-term debt supported by third-party credit enhancements |  | 103 | $ 103
Gain on CMS Energy common stock | $ 9 |  |
DB SERP [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Company contributions |  | 25 |
DB SERP [Member] | Consumers Energy Company [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Company contributions |  | $ 17 |

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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