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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
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Oct. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Apr. 30, 2016 USD ($) item site | Mar. 31, 2016 USD ($) | Jan. 31, 2016 USD ($) | Nov. 30, 2015 USD ($) | Jul. 31, 2015 USD ($) | Jun. 30, 2015 USD ($) site | Dec. 31, 2014 USD ($) | Dec. 31, 2016 USD ($) site | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Sep. 30, 2015 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) site | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Mar. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | $ 1,640 | $ 1,587 | $ 1,371 | $ 1,801 | $ 1,509 | $ 1,486 | $ 1,350 | $ 2,111 | $ 6,399 |  | $ 6,456 |  | $ 7,179 |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  | 95 |  |  |  | 82 |  |  |  | 95 |  | 82 |  |  |  |
Accrued rate refunds |  |  |  |  |  |  |  |  |  | 21 |  |  |  | 26 |  |  |  | 21 |  | 26 |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 710 |  | 961 |  | 1,493 |  |
Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax benefits returned to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 64 |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 1,550 | 1,498 | 1,293 | 1,723 | 1,439 | $ 1,417 | $ 1,281 | 2,028 | 6,064 |  | 6,165 |  | 6,800 |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  | 95 |  |  |  | 82 |  |  |  | $ 95 |  | 82 |  |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |
Accrued rate refunds |  |  |  |  |  |  |  |  |  | 21 |  |  |  | 26 |  |  |  | $ 21 |  | 26 |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 693 |  | 939 |  | 1,375 |  |
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units 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 |  |  |  |  |  |
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 Cost Recover (GCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery requested |  |  |  | $ 2 |  |  |  |  |  |  |  |  | $ 2 |  |  |  |  |  | $ 2 |  |  |  |  |
Accrued rate refunds |  |  |  |  |  |  |  |  |  | 13 |  |  |  | 18 |  |  |  | $ 13 |  | 18 |  |  |  |
Over (under) recovery authorized by the MPSC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9 |  |  |  | $ 9 |  | $ (84) |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500 |  | $ 800 |  | $ 900 |
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery requested |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  | 6 |  |  |  |
Litigation costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  |
Accrued rate refunds |  |  |  |  |  |  |  |  |  | 8 |  |  |  | 8 |  |  |  | 8 |  | 8 |  |  |  |
PSCR Cost of Power Sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,900 |  | 2,100 |  | $ 1,900
Over (under) recovery authorized by the MPSC |  |  |  |  |  |  |  |  | $ 5 |  |  |  |  |  |  |  |  |  |  |  |  | $ 5 |  | 9
Energy Optimization [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized recovery/collection |  | $ 18 |  |  |  |  |  |  |  |  | $ 18 |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18 |  | 18 |  |  |  |
Requested recovery/collection |  |  |  |  |  |  |  |  |  | $ 18 |  |  |  |  |  |  |  | $ 18 |  |  |  |  |  |
2014 Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units retired | item |  |  | 7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2016 Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amended Annual Rate Increase Request | $ 208 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  | $ 225 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  | 10.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase self-implemented |  | $ 170 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2017 |  |  |  | $ 38 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2018 |  |  |  | 92 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment recovery, 2019 |  |  |  | $ 92 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | 23 |  |  |  |  |  |
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized recovery, collection period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |
Renewable Energy Grant [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from government grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69
Revenue Subject To Refund [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  | $ 31 |  |  |  | 18 |  |  |  | $ 31 |  | 18 |  |  |  |
Revenue Subject To Refund [Member] | Gas Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  | $ 10 |  |  |  |  |  |  |  | $ 10 |  |  |  |  |  |
Revenue Subject To Refund [Member] | 2014 Electric Rate Case [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  |  |  |  |  |  |  |
Revenue Subject To Refund [Member] | Securitized Costs [Member] | Consumers Energy Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability current |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14 |  |  |  |  |  | $ 14 |  |  |  |

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