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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2018 USD ($)
Debt Instrument [Line Items] |  |  |  |
Principal balance | $ 1,000 |  | $ 1,000 |
Debt retirement, principal |  |  | 643 |
Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal balance | 550 |  | 550 |
Debt retirement, principal |  |  | 318 |
First mortgage bonds | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal balance | $ 550 |  | $ 550 |
Interest Rate | 4.05% |  | 4.05% |
Debt issuance date |  |  | May 2018 |
Maturity Date |  |  | 2048-05 |
Tax-exempt pollution control revenue bonds | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal |  |  | $ 68 |
Maturity Date |  |  | 2018-04 |
Debt retirement date |  |  | April 2018 |
First mortgage bonds | Consumers Energy Company |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal |  |  | $ 250 |
Interest Rate | 5.65% |  | 5.65% |
Maturity Date |  |  | 2018-09 |
Debt retirement date |  |  | May 2018 |
CMS Energy Corporation |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal balance | $ 450 | [1] | $ 450 | [1]
Debt retirement, principal |  |  | 325 |
CMS Energy Corporation | Junior subordinated notes 5.625% due March 2078 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal balance | $ 200 | [1] | $ 200 | [1]
Interest Rate | 5.625% | [1] | 5.625% | [1]
Debt issuance date |  |  | March 2018 | [1]
Maturity Date | 2078-03 | [1] | 2078-03 | [1]
CMS Energy Corporation | Junior subordinated notes 5.875% due October 2078 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal balance | $ 250 | [1] | $ 250 | [1]
Interest Rate | 5.875% | [1] | 5.875% | [1]
Debt issuance date |  |  | September 2018 | [1]
Maturity Date |  |  | 2078-10 | [1]
CMS Energy Corporation | Term loan facility due December 2018 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal |  |  | $ 180 |
Maturity Date | 2018-12 |  | 2018-12 |
Debt retirement date |  |  | March 2018 |
CMS Energy Corporation | Term loan facility due August 2018 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal |  |  | $ 45 |
Maturity Date |  |  | 2018-12 |
Debt retirement date |  |  | August 2018 |
CMS Energy Corporation | Senior notes 8.75% due June 2019 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal |  |  | $ 100 | [2]
Interest Rate | 8.75% | [2] | 8.75% | [2]
Maturity Date |  |  | 2019-06 | [2]
Debt retirement date |  |  | June 2018 | [2]
Loss on extinguishment of debt |  |  | $ 5 |
[1] | These unsecured obligations rank subordinate and junior in right of payment to all of CMS Energy’s existing and future senior indebtedness.
[2] | CMS Energy retired these senior notes at a premium and recorded a loss on extinguishment of $5 million in other expense on its consolidated statements of income.

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