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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Sep. 30, 2016 USD ($) | Apr. 30, 2016 USD ($) item | Mar. 31, 2016 USD ($) | Jan. 31, 2016 USD ($) | Nov. 30, 2015 USD ($) | Jul. 31, 2015 USD ($) | Jun. 30, 2015 USD ($) | Dec. 31, 2014 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($) | Jun. 30, 2016 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current | $ 80 |  |  |  |  |  |  |  | $ 80 |  | $ 80 |  | $ 82 |
Operating Revenue |  |  |  |  |  |  |  |  | 1,587 | $ 1,486 | 4,759 | $ 4,947 |  |
Accrued rate refunds | 33 |  |  |  |  |  |  |  | 33 |  | 33 |  | 26 |
Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current | 80 |  |  |  |  |  |  |  | 80 |  | 80 |  | 82 |
Operating Revenue |  |  |  |  |  |  |  |  | 1,498 | $ 1,417 | 4,514 | $ 4,726 |  |
Accrued rate refunds | 33 |  |  |  |  |  |  |  | 33 |  | 33 |  | 26 |
Consumers Energy Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in net plant, property, and equipment |  | $ 34 |  |  |  |  |  |  |  |  |  |  |  |
2014 Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  | $ 163 |  |  |  |  |  |
Annual rate increase self-implemented |  |  |  |  |  |  | $ 110 |  |  |  |  |  |  |
Annual rate increase authorized |  | $ 126 |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  | 10.30% |  |  |  |  |  |  |  |  |
Temporary rate increase |  |  |  |  | $ 165 |  |  |  |  |  |  |  |  |
Number of units retired | item |  | 7 |  |  |  |  |  |  |  |  |  |  |  |
2014 Electric Rate Case [Member] | Self-Implemented Rate Refunds [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1
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% |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2017 |  |  | $ 38 |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2018 |  |  | 92 |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2019 |  |  | $ 92 |  |  |  |  |  |  |  |  |  |  |
Annual rate increase self-implemented | 170 |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  | $ 85 |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  | 10.70% |  |  |  |  |  |  |  |
Annual rate increase self-implemented |  |  |  | $ 60 |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  | $ 40 |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case [Member] | Self-Implemented Rate Refunds [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current | 10 |  |  |  |  |  |  |  | 10 |  | 10 |  |  |
Energy Optimization Plan Incentive [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | $ 18 |
Authorized recovery/collection | $ 18 |  |  |  |  |  |  |  | $ 18 |  | 18 |  |  |
Current FERC Revenue Requirement [Member] | Consumers Energy Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue requirement |  |  |  |  |  |  |  |  |  |  | 9 |  |  |
METC Proposed FERC Revenue Requirement [Member] | Consumers Energy Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue requirement |  |  |  |  |  |  |  |  |  |  | 6 |  |  |
2016 PSCR [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation costs |  |  |  |  |  |  |  |  |  |  | $ 6 |  |  |

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