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Regulatory Matters (Schedule of the Components of the Annual Rate Increase Authorized and Requested) (Details) (2010 Gas Rate Case [Member], Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified | 1 Months Ended |
--- | --- | ---
May 31, 2011 | Aug. 31, 2010
Annual Rate Increase Authorized by the MPSC | $ 31 |
Annual Rate Increase Requested by Consumers |  | 55
Difference Between Annual Rate Increase Authorized and Annual Rate Increase Requested | (24) |
Investment in Rate Base [Member] |  |
Annual Rate Increase Authorized by the MPSC | 29 |
Annual Rate Increase Requested by Consumers |  | 30
Difference Between Annual Rate Increase Authorized and Annual Rate Increase Requested | (1) |
Impact Of Sales Declines [Member] |  |
Annual Rate Increase Authorized by the MPSC | 15 |
Annual Rate Increase Requested by Consumers |  | 4
Difference Between Annual Rate Increase Authorized and Annual Rate Increase Requested | 11 |
Operating And Maintenance Costs [Member] |  |
Annual Rate Increase Authorized by the MPSC | 2 |
Annual Rate Increase Requested by Consumers |  | 16
Difference Between Annual Rate Increase Authorized and Annual Rate Increase Requested | (14) |
Cost Of Capital [Member] |  |
Annual Rate Increase Authorized by the MPSC | (15) |
Annual Rate Increase Requested by Consumers |  | 5
Difference Between Annual Rate Increase Authorized and Annual Rate Increase Requested | $ (20) |

X
- Definition The annual rate increase authorized by the MPSC. + References No definition available. + Details
Name: | cms_AnnualRateIncreaseAuthorized
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The annual rate increase requested by Consumers. + References No definition available. + Details
Name: | cms_AnnualRateIncreaseRequested
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The difference between the amount of the annual rate increase requested by Consumers and the amount of the annual rate increase authorized by the MPSC. + References No definition available. + Details
Name: | cms_DifferenceBetweenAnnualRateIncreaseAuthorizedAndRequested
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration