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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2017 | Feb. 28, 2017 | Jan. 31, 2017 | Sep. 30, 2016 | Aug. 31, 2016 | Mar. 31, 2016 | Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Regulatory liability current | $ 85 |  |  |  |  |  | $ 85 |  | $ 95
Accrued rate refunds | 73 |  |  |  |  |  | 73 |  | 21
Revenue |  |  |  |  |  |  | 1,829 | $ 1,801 |
Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Regulatory liability current | 85 |  |  |  |  |  | 85 |  | 95
Accrued rate refunds | 73 |  |  |  |  |  | 73 |  | 21
Revenue |  |  |  |  |  |  | 1,737 | $ 1,723 |
2016 Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  | $ 225 |  |  |
Rate of return on equity requested |  |  |  |  |  | 10.70% |  |  |
Annual rate increase self-implemented |  |  |  | $ 170 |  |  |  |  |
Annual rate increase authorized |  | $ 113 |  |  |  |  |  |  |
Rate of return on equity authorized |  | 10.10% |  |  |  |  |  |  |
2016 Electric Rate Case [Member] | Revenue Subject To Refund [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Regulatory liability current | 16 |  |  |  |  |  | 16 |  |
Gas Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  | $ 90 |  |  |  |
Amended Annual Rate Increase Request | 80 |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  | 10.60% |  |  |  |
Investment recovery, 2018 |  |  |  |  | $ 35 |  |  |  |
Investment recovery, 2019 |  |  |  |  | $ 35 |  |  |  |
Annual rate increase self-implemented |  |  | $ 20 |  |  |  |  |  |
Gas Rate Case [Member] | Consumers Energy Company [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Annual rate increase self-implemented |  |  | $ 20 |  |  |  |  |  |
Energy Optimization [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Requested recovery/collection | 18 |  |  |  |  |  | $ 18 |  |
Revenue |  |  |  |  |  |  |  |  | $ 18
Depreciation Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Annual rate increase authorized | $ (3) |  |  |  |  |  |  |  |
FERC Transmission Order [Member] | Consumers Energy Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  | 10.32% | 12.38% |  |  |  |
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Accrued rate refunds |  | $ 28 |  |  |  |  |  |  |

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