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.