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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions | Jun. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Current notes receivable |  | $ 114 | $ 98
Current portion of long-term debt |  | 498 | 519
Carrying Amount [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Securities held to maturity - Fair Value |  | 13 | 11
Long-term debt, Fair Value | [1] | 8,538 | 8,535
Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Securities held to maturity - Fair Value |  | 13 | 11
Long-term debt, Fair Value | [1] | 9,090 | 9,285
Consumers Energy Company [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Current portion of long-term debt |  | 100 | 124
Consumers Energy Company [Member] | Carrying Amount [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [2] | 5,241 | 5,278
Consumers Energy Company [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [2] | 5,567 | 5,749
EnerBank [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Current notes receivable |  | 113 | 138
EnerBank [Member] | Carrying Amount [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Notes receivable, Fair Value | [3] | 990 | 938
EnerBank [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Notes receivable, Fair Value | [3] | $ 1,052 | $ 995
Fair Value, Inputs, Level 1 [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Securities held to maturity - Fair Value |  |  |
Long-term debt, Fair Value | [1] |  |
Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [2] |  |
Fair Value, Inputs, Level 1 [Member] | EnerBank [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Notes receivable, Fair Value | [3] |  |
Fair Value, Inputs, Level 2 [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Securities held to maturity - Fair Value |  | $ 13 | $ 11
Long-term debt, Fair Value | [1] | 8,088 | 8,252
Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [2] | 4,565 | 4,716
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [1] | 1,002 | 1,033
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term debt, Fair Value | [2] | 1,002 | 1,033
Fair Value, Inputs, Level 3 [Member] | EnerBank [Member] | Fair Value [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Notes receivable, Fair Value | [3] | $ 1,052 | $ 995
[1] | Includes current portion of long-term debt of $498 million at June 30, 2015 and $519 million at December 31, 2014.
[2] | Includes current portion of long-term debt of $100 million at June 30, 2015 and $124 million at December 31, 2014.
[3] | Includes current portion of notes receivable of $113 million at June 30, 2015 and $138 million at December 31, 2014.

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- 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
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- Definition Fair value of investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 + Details
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- Definition Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19,20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition An amount representing an agreement for an unconditional promise by the maker to pay the Company (holder) a definite sum of money within one year from the balance sheet date (or the normal operating cycle, whichever is longer), net of any write-downs taken for collection uncertainty on the part of the holder. Such amount may include accrued interest receivable in accordance with the terms of the debt. The debt also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. This amount does not include amounts related to receivables held-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4531-111522 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765 + Details
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