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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 2,480 |  |
Debt retirement, principal | 1,793 |  |
Loss on extinguishment | 16 | $ 18 | $ 18
Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | 1,168 |  |
Tax-exempt pollution control revenue bond | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 68 |  |
Debt retirement date | April 2018 |  |
Maturity date | 2018-04 |  |
FMB's 5.650% Due 2018 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 250 |  |
Interest rate | 5.65% |  |
Debt retirement date | May 2018 |  |
Maturity date | 2018-09 |  |
FMB's 6.125% Due 2019 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 350 |  |
Interest rate | 6.125% |  |
Debt retirement date | November 2018 |  |
Maturity date | 2019-03 |  |
FMB's 6.700% Due 2019 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 500 |  |
Interest rate | 6.70% |  |
Debt retirement date | November 2018 |  |
Maturity date | 2019-09 |  |
Term loans and revolving credit agreements |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 100 |  |
Term loans and revolving credit agreements | Term Loan Facility Due 2019 |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 100 |  |
Debt issuance date | October 2018 |  |
Maturity date | 2025-09 |  |
First Mortgage Bonds | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 1,900 |  |
First Mortgage Bonds | FMB's 4.050% Due 2048 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 550 |  |
Interest rate | 4.05% |  |
Debt issuance date | May 2018 |  |
Maturity date | 2048-05 |  |
First Mortgage Bonds | FMB's 3.680% Due 2027 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 100 |  |
Interest rate | 3.68% |  |
Debt issuance date | October 2018 |  |
Maturity date | 2027-10 |  |
First Mortgage Bonds | FMB's 4.010% Due 2038 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 215 |  |
Interest rate | 4.01% |  |
Debt issuance date | October 2018 |  |
Maturity date | 2038-10 |  |
First Mortgage Bonds | FMB's 4.280% Due 2057 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 185 |  |
Interest rate | 4.28% |  |
Debt issuance date | October 2018 |  |
Maturity date | 2057-10 |  |
First Mortgage Bonds | FMB's 3.800% Due 2028 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 300 |  |
Interest rate | 3.80% |  |
Debt issuance date | November 2018 |  |
Maturity date | 2028-11 |  |
First Mortgage Bonds | FMB's 4.350% Due 2049 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 550 |  |
Interest rate | 4.35% |  |
Debt issuance date | November 2018 |  |
Maturity date | 2049-04 |  |
First Mortgage Bonds | FMB's 5.650% Due 2018 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate | 5.65% |  |
First Mortgage Bonds | FMB's 6.125% Due 2019 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate | 6.125% |  |
First Mortgage Bonds | FMB's 6.700% Due 2019 | Consumers Energy Company |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate | 6.70% |  |
CMS Energy |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 625 |  |
CMS Energy | Term Loan Facility Due March 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 180 |  |
Debt retirement date | March 2018 |  |
Maturity date | 2018-12 |  |
CMS Energy | Senior Notes 8.750% Due 2019 |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 100 |  |
Interest rate | 8.75% |  |
Debt retirement date | June 2018 |  |
Maturity date | 2019-06 |  |
Loss on extinguishment | $ 5 |  |
CMS Energy | Term Loan Facility Due August 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 45 |  |
Debt retirement date | August 2018 |  |
Maturity date | 2018-12 |  |
CMS Energy | Senior Notes 6.250% Due 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Debt retirement, principal | $ 300 |  |
Interest rate | 6.25% |  |
Debt retirement date | October 2018 |  |
Maturity date | 2020-02 |  |
Loss on extinguishment | $ 11 |  |
CMS Energy | Junior subordinated notes |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | 480 |  |
CMS Energy | Junior subordinated notes | Junior Notes 5.625% Due 2078 |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 200 |  |
Interest rate | 5.625% |  |
Debt issuance date | March 2018 |  |
Maturity date | 2078-03 |  |
CMS Energy | Junior subordinated notes | Junior Notes 5.875% Due 2078 |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 250 |  |
Interest rate | 5.875% |  |
Debt issuance date | September 2018 |  |
Maturity date | 2078-10 |  |
CMS Energy | Junior subordinated notes | Junior Notes 5.875% Due 2078 |  |  |
Debt Instrument [Line Items] |  |  |
Principal Balance | $ 30 |  |
Interest rate | 5.875% |  |
Debt issuance date | October 2018 |  |
Maturity date | 2078-10 |  |
CMS Energy | Senior notes | Senior Notes 8.750% Due 2019 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate | 8.75% |  |
CMS Energy | Senior notes | Senior Notes 6.250% Due 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate | 6.25% |  |

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