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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Apr. 30, 2016 USD ($) | Dec. 31, 2015 USD ($) site | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Sep. 30, 2015 USD ($) | Nov. 30, 2014 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Proceeds from government grant |  |  |  | $ 69 |  |
Accrued rate refunds |  | $ 26 | $ 6 |  |  |
Cost of gas sold |  | 961 | 1,493 | 1,228 |  |
Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits returned to customers |  | $ 64 |  |  |  |
Proceeds from government grant |  |  |  | 69 |  |
Number of units planned to be retired | site |  | 10 |  |  |  |
Accrued rate refunds |  | $ 26 | 6 |  |  |
Cost of gas sold |  | $ 939 | 1,375 | 1,187 |  |
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Number of units planned to be retired | site |  | 7 |  |  |  |
Gas-Fueled Electric Generation [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Number of units retired | site |  | 3 |  |  |  |
Electric Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits, to be returned to customers |  | $ 209 |  |  |  |
Tax benefit, distribution to customers, term |  | 5 years |  |  |  |
Gas Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits, to be returned to customers |  | $ 260 |  |  |  |
Tax benefit, distribution to customers, term |  | 12 years |  |  |  |
Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Annual rate increase requested |  |  | $ 163 |  |  |
Rate of return on equity requested |  |  | 10.70% |  |  |
Annual rate increase self-implemented |  | $ 110 |  |  |  |
Annual rate increase authorized |  | $ 165 |  |  |  |
Rate of return on equity authorized |  | 10.30% |  |  |  |
Depreciation Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Annual rate increase requested |  |  | $ 28 |  |  |
Annual rate increase authorized |  | $ 6 |  |  |  |
Gas Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Annual rate increase requested |  |  | 88 |  |  |
Annual rate increase authorized |  | $ 45 |  |  |  |
Rate of return on equity authorized |  | 10.30% |  |  |  |
Gas Cost Recover (GCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Over (under) recovery requested |  | $ 9 | (84) |  |  |
Accrued rate refunds |  | 18 |  |  |  |
Cost of gas sold |  | 800 | 900 |  |  |
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Over (under) recovery requested |  | 6 | 10 |  |  |
Accrued rate refunds |  | 8 |  |  |  |
PSCR Cost of Power Sold |  | 2,100 | $ 1,900 |  |  |
Energy Optimization [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery/collection |  |  |  |  | $ 17 |
Requested recovery/collection |  | $ 18 |  |  |  |
Major Maintenance [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period |  | 6 months |  |  |  |
Authorized recovery/collection |  |  |  |  |  | $ 10
Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period |  | 10 years |  |  |  |
Number of former MGPs | site |  | 23 |  |  |  |
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period |  | 5 years |  |  |  |
Scenario, Forecast [Member] | Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Change in annual rate increase authorized | $ 39 |  |  |  |  |
Annual rate increase authorized | $ 126 |  |  |  |  |
Renewable Energy Grant [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Proceeds from government grant |  |  |  | $ 69 |  |

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