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Notes Receivable (Schedule Of Allowance For Loan Losses) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Allowance for loan losses, at beginning of period | $ 5 us-gaap_FinancingReceivableAllowanceForCreditLosses | $ 5 us-gaap_FinancingReceivableAllowanceForCreditLosses
Charge-offs | (6)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs | (5)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Recoveries | 1 us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery | 1 us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Provision for loan losses | 8 us-gaap_ProvisionForLoanLeaseAndOtherLosses | 4 us-gaap_ProvisionForLoanLeaseAndOtherLosses
Allowance for loan losses, at end of period | 8 us-gaap_FinancingReceivableAllowanceForCreditLosses | 5 us-gaap_FinancingReceivableAllowanceForCreditLosses
EnerBank [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Delinquent loans | 5 us-gaap_FinancingReceivableRecordedInvestmentPastDue / dei_LegalEntityAxis = cms_EnerBankMember | 4 us-gaap_FinancingReceivableRecordedInvestmentPastDue / dei_LegalEntityAxis = cms_EnerBankMember
Loans modified as troubled debt restructurings | $ 1 us-gaap_FinancingReceivableModificationsRecordedInvestment / dei_LegalEntityAxis = cms_EnerBankMember | $ 1 us-gaap_FinancingReceivableModificationsRecordedInvestment / dei_LegalEntityAxis = cms_EnerBankMember

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- Definition A valuation allowance for financing receivables that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
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- Definition Amount of recovery of financing receivables doubtful of collection that were previously charged off. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
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- Definition Amount of direct write-downs of financing receivables charged against the allowance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
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- Definition The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554 + Details
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- Definition Recorded Investment in financing receivables that are past due at the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524 + Details
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- Definition Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 11 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.11) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
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