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Financings and Capitalization (Narrative) (Details) - USD ($) |  | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2019 | Dec. 31, 2018 | Oct. 24, 2019
Financing And Capitalization [Line Items] |  |  |  |
Principal balance | $ 2,021,000,000 | $ 2,021,000,000 |  |
Amount available for dividend payments | $ 5,000,000,000.0 | 5,000,000,000.0 |  |
Common stock dividends from Consumers |  | $ 396,000,000 |  |
Stock offering program maximum value |  |  | $ 250,000,000 |
Settlement required (in shares) | 1,039,414 | 1,039,414 |  |
Consumers Energy Company |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Principal balance | $ 926,000,000 | $ 926,000,000 |  |
Unrestricted retained earnings | 1,400,000,000 | 1,400,000,000 |  |
Consumers Energy Company | Commercial Paper |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Short-term debt, authorized borrowings |  | 500,000,000 |  |
Short-term debt | 0 | $ 0 |  |
Forward Contracts |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Forward sales contracts aggregate price | $ 250,000,000 |  |  |
Michigan Strategic Fund Loan Agreement | Subsequent Event | Loan Agreement | Consumers Energy Company |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Principal balance |  |  |  | $ 75,000,000
Michigan Strategic Fund | MIchigan Strategic Fund Bonds | Subsequent Event | Variable Rate Revenue Bonds | Consumers Energy Company |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Principal balance |  |  |  | $ 75,000,000

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