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Plant, Property, and Equipment (Schedule of Finite-Lived Intangible Assets by Major Class Table) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | $ 930 | $ 787
Finite-Lived Intangible Assets, Accumulated Amortization |  | 368 | 293
Public Utilities, Property Plant and Equipment Additions |  | 1,400 | 1,600
Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 925 | 785
Finite-Lived Intangible Assets, Accumulated Amortization |  | 365 | 291
Public Utilities, Property Plant and Equipment Additions |  | 1,400 | 1,600
Software and Software Development Costs [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 734 | 596
Finite-Lived Intangible Assets, Accumulated Amortization |  | 294 | 223
Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 729 | 594
Finite-Lived Intangible Assets, Accumulated Amortization |  | 291 | 221
Leasehold Improvements [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1],[2] | 7 | 5
Finite-Lived Intangible Assets, Accumulated Amortization | [2] | 5 | 4
Leasehold Improvements [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1],[2] | 7 | 5
Finite-Lived Intangible Assets, Accumulated Amortization | [2] | 5 | 4
Intangible Plant [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Public Utilities, Property Plant and Equipment Additions |  | 140 | 96
Rights of Way [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 153 | 150
Finite-Lived Intangible Assets, Accumulated Amortization |  | 46 | 44
Rights of Way [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 153 | 150
Finite-Lived Intangible Assets, Accumulated Amortization |  | 46 | 44
Franchises and Consents [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 15 | 15
Finite-Lived Intangible Assets, Accumulated Amortization |  | 8 | 8
Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 15 | 15
Finite-Lived Intangible Assets, Accumulated Amortization |  | 8 | 8
Other Intangible Assets [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 21 | 21
Finite-Lived Intangible Assets, Accumulated Amortization |  | 15 | 14
Other Intangible Assets [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 21 | 21
Finite-Lived Intangible Assets, Accumulated Amortization |  | $ 15 | $ 14
Minimum [Member] | Software and Software Development Costs [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 2 years |
Minimum [Member] | Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 3 years |
Minimum [Member] | Rights of Way [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 50 years |
Minimum [Member] | Rights of Way [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 50 years |
Minimum [Member] | Franchises and Consents [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 5 years |
Minimum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 5 years |
Maximum [Member] | Software and Software Development Costs [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 15 years |
Maximum [Member] | Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 15 years |
Maximum [Member] | Rights of Way [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 75 years |
Maximum [Member] | Rights of Way [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 75 years |
Maximum [Member] | Franchises and Consents [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 30 years |
Maximum [Member] | Franchises and Consents [Member] | Consumers Energy Company [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Finite-Lived Intangible Asset, Useful Life |  | 30 years |
[1] | Net intangible asset additions for Consumers' utility plant were $140 million during 2015 and $96 million during 2014 and primarily represented software development costs.
[2] | Leasehold improvements are amortized over the life of the lease, which may change whenever the lease is renewed or extended.

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- 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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