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Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2017 USD ($) item lawsuit | Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items] |  |
Regulatory assets | $ 2,050 | $ 2,091
Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Regulatory assets | 2,050 | $ 2,091
Bay Harbor [Member] |  |
Loss Contingencies [Line Items] |  |
Demand for payment by USEPA | 8 |
Accrual for environmental loss contingencies | $ 50 |
Discounted projected costs rate | 4.34% |
Remaining undiscounted obligation amount | $ 63 |
Accrual for environmental loss contingencies, inflation rate | 1.00% |
Electric Utility [Member] | NREPA [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | $ 3 |
Electric Utility [Member] | NREPA [Member] | Minimum [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 3 |
Electric Utility [Member] | NREPA [Member] | Maximum [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 4 |
Electric Utility [Member] | CERCLA Liability [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | 3 |
Electric Utility [Member] | CERCLA Liability [Member] | Minimum [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 3 |
Electric Utility [Member] | CERCLA Liability [Member] | Maximum [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 8 |
Gas Utility [Member] | NREPA [Member] | Maximum [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | 1 |
Remediation and other response activity costs | 3 |
Gas Utility [Member] | Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | $ 98 |
Discounted projected costs rate | 2.57% |
Remaining undiscounted obligation amount | $ 107 |
Number of former MGPs | item | 23 |
Regulatory assets | $ 137 |
Authorized recovery, collection period | 10 years |
Accrual for environmental loss contingencies, inflation rate | 2.50% |
Equatorial Guinea Tax Claim [Member] |  |
Loss Contingencies [Line Items] |  |
Foreign government tax claim on sale | $ 152 |
Class Action Lawsuits [Member] |  |
Loss Contingencies [Line Items] |  |
Number of lawsuits | lawsuit | 4 |
Individual Lawsuits [Member] |  |
Loss Contingencies [Line Items] |  |
Number of lawsuits | lawsuit | 1 |

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