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Financings And Capitalization (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Oct. 25, 2018 | Aug. 31, 2018 | Mar. 31, 2017 | Sep. 30, 2018 | Jul. 31, 2018
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  |  |  |  | $ 1,000 |
Debt retirement, principal |  |  |  |  | 643 |
Unrestricted retained earnings |  |  |  |  | 4,700 |
Common stock dividends from Consumers |  |  |  |  | 392 |
Stock offering program maximum value |  |  | $ 250 | $ 100 |  |
Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  |  |  |  | 550 |
Debt retirement, principal |  |  |  |  | 318 |
Unrestricted retained earnings |  |  |  |  | 1,300 |
Consumers Energy Company | Commercial Paper |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Short-term debt, authorized borrowings |  |  |  |  | 500 |
Short-term debt |  |  |  |  | 279 |
October 2018 First Mortgage Bonds | Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  |  |  |  |  | $ 500
Subsequent Event | 3.68% First Mortgage Bonds Due 2027 | Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  | $ 100 |  |  |  |
Interest Rate |  | 3.68% |  |  |  |
Subsequent Event | 4.01% First Mortgage Bonds Due 2038 | Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  | $ 215 |  |  |  |
Interest Rate |  | 4.01% |  |  |  |
Subsequent Event | 4.28% First Mortgage Bonds Due 2057 | Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  | $ 185 |  |  |  |
Interest Rate |  | 4.28% |  |  |  |
CMS Energy Corporation |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance | [1] |  |  |  | 450 |
Debt retirement, principal |  |  |  |  | $ 325 |
CMS Energy Corporation | Subsequent Event | 5.875% Junior Subordinated Notes Due 2078 |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Principal balance |  | $ 30 |  |  |  |
Interest Rate | [1] | 5.875% |  |  |  |
CMS Energy Corporation | Subsequent Event | 6.25% Senior Notes Due 2020 |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Interest Rate | [1] | 6.25% |  |  |  |
Loss on extinguishment of debt |  | $ 11 |  |  |  |
Debt retirement, principal |  | $ 300 |  |  |  |
[1] | These unsecured obligations rank subordinate and junior in right of payment to all of CMS Energy’s existing and future senior indebtedness.

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