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Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 USD ($) lawsuit site | Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items] |  |
Regulatory assets | $ 1,690 | $ 1,764
Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Regulatory assets | 1,690 | $ 1,764
Bay Harbor |  |
Loss Contingencies [Line Items] |  |
Demand for payment by USEPA | 8 |
Accrual for obligations for environmental remediation | $ 47 |
Discounted projected costs rate | 4.34% |
Remaining undiscounted obligation amount | $ 58 |
Accrual for environmental loss contingencies, inflation rate | 1.00% |
Electric Utility | NREPA | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Accrual for obligations for environmental remediation | $ 3 |
Electric Utility | NREPA | Minimum | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 3 |
Electric Utility | NREPA | Maximum | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 4 |
Electric Utility | CERCLA Liability | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Accrual for obligations for environmental remediation | 3 |
Electric Utility | CERCLA Liability | Minimum | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 3 |
Electric Utility | CERCLA Liability | Maximum | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | 8 |
Gas Utility | NREPA | Maximum | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Accrual for obligations for environmental remediation | 1 |
Remediation and other response activity costs | 3 |
Gas Utility | Manufactured Gas Plant | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Accrual for obligations for environmental remediation | $ 83 |
Discounted projected costs rate | 2.57% |
Remaining undiscounted obligation amount | $ 90 |
Number of former MGPs | site | 23 |
Regulatory assets | $ 139 |
Authorized recovery, collection period | 10 years |
Accrual for environmental loss contingencies, inflation rate | 2.50% |
Equatorial Guinea Tax Claim |  |
Loss Contingencies [Line Items] |  |
Foreign government tax claim on sale | $ 152 |
Class Action Lawsuits |  |
Loss Contingencies [Line Items] |  |
Number of lawsuits | lawsuit | 4 |
Individual Lawsuits |  |
Loss Contingencies [Line Items] |  |
Number of lawsuits | lawsuit | 1 |
MCV PPA | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | $ 270 |
Underwater cables Straits of Mackinac [Member] | Consumers Energy Company |  |
Loss Contingencies [Line Items] |  |
Remediation and other response activity costs | $ 10 |

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