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Related Party Transactions - Consumers (Details) - Consumers Energy Company - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Related Party Transaction [Line Items] |  |  |
Purchased power – related parties | $ 64,000,000 | $ 75,000,000 | $ 83,000,000
Due to related parties | 13,000,000 | 26,000,000 |
Accounts receivable related parties | 16,000,000 | 8,000,000 |
Investments |  | 1,000,000 |
Notes payable – related parties | 307,000,000 | $ 0 |
Credit Agreement |  |  |
Related Party Transaction [Line Items] |  |  |
Maximum borrowing capacity | 350,000,000 |  |
Notes payable – related parties | $ 307,000,000 |  |
Weighted average interest rate | 0.042% |  |
Natural Gas Transportation Agreement | CMS Energy Subsidiary |  |  |
Related Party Transaction [Line Items] |  |  |
Direct financing lease term | 20 years |  |

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