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Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended |  |  |  |  |  |  | 1 Months Ended
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Sep. 30, 2013 | Dec. 31, 2012 | Oct. 31, 2010 | Sep. 30, 2013 Consumers Energy Company [Member] | Dec. 31, 2012 Consumers Energy Company [Member] | Sep. 30, 2013 NREPA [Member] Consumers Energy Company [Member] | Sep. 30, 2013 Superfund Liability [Member] Consumers Energy Company [Member] | Sep. 30, 2013 Manufactured Gas Plant [Member] Consumers Energy Company [Member] item | Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member] | Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |
Demand for payment by USEPA |  |  | $ 7 |  |  |  |  |  |  |
Cumulative environmental charge | 228 |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies | 55 |  |  |  |  | 4 | 2 | 121 |  |
Discounted projected costs rate | 4.34% |  |  |  |  |  |  | 2.57% |  |
Accrual for environmental loss contingencies, inflation rate | 1.00% |  |  |  |  |  |  | 2.50% |  |
Remaining undiscounted obligation amount | 73 |  |  |  |  |  |  | 131 |  |
Foreign government tax claim on sale | 142 |  |  |  |  |  |  |  |  |
Remediation and other response activity costs, minimum |  |  |  |  |  | 4 | 2 |  |  |
Remediation and other response activity costs. maximum |  |  |  |  |  | 6 | 8 |  |  |
Litigation settlement, gross |  |  |  |  |  |  |  |  |  | 120
Number of former MGPs |  |  |  |  |  |  |  | 23 |  |
Regulatory assets, noncurrent | $ 1,579 | $ 2,287 |  | $ 1,579 | $ 2,287 |  |  | $ 150 | $ 85 |

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