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v3.20.4

Financings And Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 3,161 | $ 3,161 |  |
Debt retirement, principal |  | 1,325 |  |
Loss on extinguishment of debt |  | 16 | $ 0 | $ 16
Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | 1,961 | 1,961 |  |
Debt retirement, principal |  | 1,025 |  |
Term loans and revolving credit agreements | Term loan facility due January 2021 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | 300 | 300 |  |
Debt retirement, principal |  | 300 |  |
First Mortgage Bonds | 3.500% First Mortgage Bonds Due 2051 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 575 | $ 575 |  |
Interest rate | 3.50% | 3.50% |  |
First Mortgage Bonds | 2.500% First Mortgage Bonds Due 2060 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 525 | $ 525 |  |
Interest rate | 2.50% | 2.50% |  |
First Mortgage Bonds | Variable Rate First Mortgage Bonds Due May 2070 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 134 | $ 134 |  |
First Mortgage Bonds | Variable Rate First Mortgage Bonds Due October 2070 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | 127 | 127 |  |
First Mortgage Bonds | 0.350% First Mortgage Bonds Due 2023 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 300 | $ 300 |  |
Interest rate | 0.35% | 0.35% |  |
First Mortgage Bonds | 3.770% Percent First Mortgage Bonds Due 2020 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate | 3.77% | 3.77% |  |
Debt retirement, principal |  | $ 100 |  |
First Mortgage Bonds | 5.300% First Mortgage Bonds Due 2022 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate | 5.30% | 5.30% |  |
Debt retirement, principal |  | $ 250 |  |
First Mortgage Bonds | 2.850% First Mortgage Bonds Due 2022 | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate | 2.85% | 2.85% |  |
Debt retirement, principal |  | $ 375 |  |
CMS Energy |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 1,200 | 1,200 |  |
Debt retirement, principal |  | 300 |  |
CMS Energy | Term loans and revolving credit agreements | Term Loan Facility Due February 2021 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | 300 | $ 300 |  |
Debt retirement, principal | 100 |  |  |
Basis spread on variable rate |  | 0.50% |  |
CMS Energy | Junior subordinated notes | 4.750% Junior Subordinated Notes Due 2050 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 500 | $ 500 |  |
Interest rate | 4.75% | 4.75% |  |
Interest rate reset term |  | 5 years |  |
CMS Energy | Junior subordinated notes | 4.750% Junior Subordinated Notes Due 2050 | US Treasury (UST) Interest Rate |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  | 4.116% |  |
CMS Energy | Junior subordinated notes | 3.750% Junior Subordinated Notes Due 2050 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal Balance | $ 400 | $ 400 |  |
Interest rate | 3.75% | 3.75% |  |
Interest rate reset term |  | 5 years |  |
CMS Energy | Junior subordinated notes | 3.750% Junior Subordinated Notes Due 2050 | US Treasury (UST) Interest Rate |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  | 2.90% |  |
CMS Energy | Senior notes | 5.050% Senior Notes Due 2022 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Interest rate | 5.05% | 5.05% |  |
Debt retirement, principal |  | $ 300 |  |
Loss on extinguishment of debt |  | $ 16 |  |

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