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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) - CMS Energy [Member]
3 Months Ended
Mar. 31, 2018
USD ($)
Junior Subordinated Notes 5.625% Due March 2078 [Member]  
Debt Instrument [Line Items]  
Principal Balance $ 200,000,000 [1]
Interest rate 5.625% [1]
Debt issuance date March 2018 [1]
Maturity date 2078-03 [1]
Term Loan Facility Due 2018 [Member]  
Debt Instrument [Line Items]  
Debt retirement, principal $ 180,000,000
Debt retirement date March 2018
Maturity date 2018-12
[1] These unsecured obligations rank subordinate and junior in right of payment to all of CMS Energy's existing and future senior indebtedness.