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Financings And Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 25, 2018 | Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Financing And Capitalization [Line Items] |  |  |  |
Unrestricted retained earnings |  | $ 4,600 |  |
Common stock dividends from Consumers |  | 119 |  |
Stock Offering Program Maximum Value |  |  | $ 100 |
Number of Shares Issued |  |  |  | 1,494,371
Average Price Per Share |  |  |  | $ 47.31
Net Proceeds |  |  |  | $ 70
Consumers Energy Company [Member] |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Unrestricted retained earnings |  | 1,200 |  |
Consumers Energy Company [Member] | Commercial Paper [Member] |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Short-term debt, authorized borrowings |  | 500 |  |
Short-term borrowings outstanding |  | $ 0 |  |
Consumers Energy Company [Member] | Tax-Exempt Pollution Control Revenue Bonds [Member] | Subsequent Event [Member] |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |
Debt retirement, principal | $ 68 |  |  |

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