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Plant, Property, and Equipment (Schedule of Finite-Lived Intangible Assets by Major Class Table) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011
Finite-Lived Intangible Assets, Gross | $ 855 | [1] | $ 748 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 269 |  | 232 |
Public Utilities, Property Plant and Equipment Additions | 999 |  | 700 |
Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Assets, Gross | 853 | [1] | 746 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 269 |  | 231 |
Public Utilities, Property Plant and Equipment Additions | 999 |  | 700 |
Software and Software Development Costs [Member] |  |  |  |
Finite-Lived Computer Software, Gross | 466 | [1] | 361 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 172 |  | 142 |
Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Computer Software, Gross | 464 | [1] | 360 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 172 |  | 141 |
Plant Acquisition Adjustments [Member] |  |  |  |
Public Utilities, Property, Plant and Equipment, Plant Adjustments for Intangible Utility Plants | 214 | [1] | 214 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 27 |  | 22 |
Plant Acquisition Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |
Public Utilities, Property, Plant and Equipment, Plant Adjustments for Intangible Utility Plants | 214 | [1] | 214 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 27 |  | 22 |
Leasehold Improvements [Member] |  |  |  |
Leasehold Improvements, Gross | 13 | [1] | 11 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 10 |  | 9 |
Leasehold Improvements [Member] | Consumers Energy Company [Member] |  |  |  |
Leasehold Improvements, Gross | 13 | [1] | 11 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 10 |  | 9 |
Intangible Plant [Member] | Consumers Energy Company [Member] |  |  |  |
Public Utilities, Property Plant and Equipment Additions | 108 |  | 23 |
Rights of Way [Member] |  |  |  |
Finite-Lived Contractual Rights, Gross | 130 | [1] | 128 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 40 |  | 38 |
Rights of Way [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Contractual Rights, Gross | 130 | [1] | 128 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 40 |  | 38 |
Franchises and Consents [Member] |  |  |  |
Finite-Lived Intangible Assets, Gross | 14 | [1] | 15 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 6 |  | 7 |
Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Assets, Gross | 14 | [1] | 15 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 6 |  | 7 |
Other Intangibles [Member] |  |  |  |
Other Finite-Lived Intangible Assets, Gross | 18 | [1] | 19 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | 14 |  | 14 |
Other Intangibles [Member] | Consumers Energy Company [Member] |  |  |  |
Other Finite-Lived Intangible Assets, Gross | 18 | [1] | 18 | [1]
Finite-Lived Intangible Assets, Accumulated Amortization | $ 14 |  | $ 14 |
Minimum [Member] | Software and Software Development Costs [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 3 years |  |  |
Minimum [Member] | Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 3 years |  |  |
Minimum [Member] | Plant Acquisition Adjustments [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 40 years |  |  |
Minimum [Member] | Plant Acquisition Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 40 years |  |  |
Minimum [Member] | Rights of Way [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 50 years |  |  |
Minimum [Member] | Rights of Way [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 50 years |  |  |
Minimum [Member] | Franchises and Consents [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 5 years |  |  |
Minimum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 5 years |  |  |
Maximum [Member] | Software and Software Development Costs [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 15 years |  |  |
Maximum [Member] | Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 15 years |  |  |
Maximum [Member] | Plant Acquisition Adjustments [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 46 years |  |  |
Maximum [Member] | Plant Acquisition Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 46 years |  |  |
Maximum [Member] | Rights of Way [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 75 years |  |  |
Maximum [Member] | Rights of Way [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 75 years |  |  |
Maximum [Member] | Franchises and Consents [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 30 years |  |  |
Maximum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |  |
Finite-Lived Intangible Asset, Useful Life | 30 years |  |  |
[1] | Net intangible asset additions for Consumers’ utility plant were $108 million during 2012 and $23 million during 2011 and primarily represented software development costs.

X
- Definition Current year acquisitions of long-lived assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, certain intangible assets, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software. + References No definition available. + Details
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X
- Definition Gross carrying amount before accumulated amortization as of the balance sheet date of capitalized costs to ready software for sale or licensing, or for long-term internal use. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275 + Details
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- Definition Gross amount, at the balance sheet date, of long-lived, depreciable assets that are an addition or improvement to assets held under lease arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6812-107765 + Details
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