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Contingencies and Commitments (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  |  |  |  |  |  | 1 Months Ended |  | 12 Months Ended |  |
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Dec. 31, 2011 | Dec. 31, 2010 | Oct. 31, 2010 | Dec. 31, 2004 | Dec. 31, 2011 Consumers Energy Company [Member] | Dec. 31, 2010 Consumers Energy Company [Member] | Dec. 31, 2011 NREPA [Member] Consumers Energy Company [Member] | Dec. 31, 2011 Superfund Liability [Member] Consumers Energy Company [Member] | Jul. 31, 2011 Nuclear Fuel Disposal Cost [Member] Consumers Energy Company [Member] | Jun. 30, 2011 Nuclear Fuel Disposal Cost [Member] Consumers Energy Company [Member] | Jun. 30, 2011 Spent Nuclear Fuel Principal [Member] Consumers Energy Company [Member] | Jun. 30, 2011 Spent Nuclear Fuel Interest [Member] Consumers Energy Company [Member] | Dec. 31, 2011 Manufactured Gas Plant [Member] Consumers Energy Company [Member] | Dec. 31, 2011 Manufactured Gas Plant [Member] Consumers Energy Company [Member] | Dec. 31, 2011 MGP Sites [Member] Consumers Energy Company [Member] | Dec. 31, 2010 MGP Sites [Member] Consumers Energy Company [Member]
Demand For Payment By USEPA |  |  | $ 7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Environmental Charge | 224 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recorded liability | 77 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for Environmental Loss Contingencies |  |  |  |  |  |  | 1 | 2 |  |  |  |  | 128 |  |  |  |  |
Spent Nuclear Fuel Obligation, Noncurrent |  |  |  |  |  |  |  |  |  | 163 | 44 | 119 |  |  |  |  |  |
Discounted projected costs rate | 4.34% |  |  |  |  |  |  |  |  |  |  |  | 2.57% |  |  |  |  |
Site Contingency Accrual Inflation Rate | 1.00% |  |  |  |  |  |  |  |  |  |  |  | 2.50% |  |  |  |  |
Remaining undiscounted obligation amount | 100 |  |  |  |  |  |  |  |  |  |  |  | 142 |  |  |  |  |
Undiscounted amount due within one year | 21 |  |  |  |  |  |  |  |  |  |  |  | 14 |  |  |  |  |
Undiscounted amount due within two year | 8 |  |  |  |  |  |  |  |  |  |  |  | 12 |  |  |  |  |
Undiscounted amount due within third year | 4 |  |  |  |  |  |  |  |  |  |  |  | 12 |  |  |  |  |
Undiscounted amount due within fourth year | 4 |  |  |  |  |  |  |  |  |  |  |  | 21 |  |  |  |  |
Undiscounted amount due within five year | 5 |  |  |  |  |  |  |  |  |  |  |  | 13 |  |  |  |  |
Foreign Government Tax Claim On Sale |  |  |  | 142 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs, minimum |  |  |  |  |  |  | 1 | 2 |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs. maximum |  |  |  |  |  |  | 4 | 8 |  |  |  |  |  |  |  |  |  |
Litigation Settlement, Gross |  |  |  |  |  |  |  |  | 120 |  |  |  |  |  |  |  |  |
Regulatory assets | 2,466 | 2,093 |  |  | 2,466 | 2,093 |  |  |  |  |  |  |  |  | 156 | [1] | 58 | [1]
Regulatory Liability, Noncurrent | 1,875 | 1,988 |  |  | 1,875 | 1,988 |  |  |  |  |  |  |  |  |  |  |  |
Number of former MGPs |  |  |  |  | 23 |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in MGP Liability |  |  |  |  |  |  |  |  |  |  |  |  | 104 |  |  |  |  |
Regulatory asset |  |  |  |  | 2,467 | 2,112 |  |  |  |  |  |  |  | 156 |  |  |  |
Carrying Amounts |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum Obligation |  |  |  |  | $ 30 |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | These regulatory assets represent expenditures for which the MPSC has provided, or Consumers expects, recovery without a return on investment.

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