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Financings And Capitalization (Narrative) (Details) - USD ($) | 1 Months Ended | 12 Months Ended | 24 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 | Jul. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2019
Financing And Capitalization [Line Items] |  |  |  |  |  |
Debt retirement, principal |  |  | $ 1,325,000,000 |  |  |
Limitation on payment of stock dividends |  |  | 5,500,000,000 |  |  |
Dividends paid |  |  | $ 637,000,000 |  |  |
Common stock authorized (in shares) |  |  | 350,000,000.0 | 350,000,000.0 |  | 350,000,000.0
Par value of common stock (in dollars per share) |  |  | $ 0.01 |  |  |
Preferred stock authorized (in shares) |  |  | 10,000,000 |  |  |
Par value of preferred stock (in dollars per share) |  |  | $ 0.01 |  |  |
Issuance of common stock, net of issuance costs |  |  | $ 253,000,000 | $ 12,000,000 | $ 41,000,000 |
Stock offering program maximum value |  |  | $ 500,000,000 |  |  |
Number of shares required to settle forward contracts (in shares) |  |  | 6,666 |  |  |
Variable Interest Entity, Primary Beneficiary | Aviator Wind |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Ownership interest | 51.00% | 51.00% |  |  |  |
Debt retirement, principal | $ 492,000,000 |  |  |  |  |
Consumers Energy Company |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Debt retirement, principal |  |  | $ 1,025,000,000 |  |  |
Interest rate coverage ratio multiplier minimum to issue FMBs |  |  | 200.00% |  |  |
Unrestricted retained earnings |  |  | $ 1,600,000,000 |  |  |
Common stock authorized (in shares) |  |  | 125,000,000.0 | 125,000,000.0 |  | 125,000,000.0
Consumers Energy Company | Credit Agreement |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Maximum borrowing capacity |  |  | $ 350,000,000 |  |  |
Consumers Energy Company | Commercial Paper |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Short-term debt authorized borrowings |  |  | 500,000,000 |  |  |
Short-term borrowings outstanding |  |  | $ 0 |  |  |
Tax Exempt Revenue Bonds Due 2035 | Consumers Energy Company | Tax Exempt Revenue Bonds |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Debt repurchased |  | $ 35,000,000 |  |  |  |
Forward Contracts |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Forward contract indexed to issuer's equity |  |  |  |  |  | $ 250,000,000
Settlement Of Forward Contracts |  |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |  |
Settlement of forward contract indexed to issuer's equity (in shares) |  |  | 4,879,022 |  |  |
Settlement rate per share (in dollars per share) |  |  | $ 48.86 |  |  |
Issuance of common stock, net of issuance costs |  |  | $ 238,000,000 |  |  |

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