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, 2011 years		Dec. 31, 2010
Finite-Lived Intangible Assets, Accumulated Amortization	$ 232		$ 207
Finite-Lived Intangible Assets, Gross	748		724
Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Accumulated Amortization	231		207
Public Utilities, Property, Plant and Equipment, Plant Adjustments for Intangible Utility Plants	23		25
Finite-Lived Intangible Assets, Gross	746	[1]	722	[1]
Software and Software Development Costs [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	3
Finite-Lived Intangible Assets, Useful Life, Maximum	15
Finite-Lived Computer Software, Gross	361		323
Finite-Lived Intangible Assets, Accumulated Amortization	142		125
Software and Software Development Costs [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	3
Finite-Lived Intangible Assets, Useful Life, Maximum	15
Finite-Lived Computer Software, Gross	360	[1]	323	[1]
Finite-Lived Intangible Assets, Accumulated Amortization	141		125
Plant Acquisition Adjustments [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	40
Finite-Lived Intangible Assets, Useful Life, Maximum	46
Finite-Lived Intangible Assets, Accumulated Amortization	22		16
Public Utilities, Property, Plant and Equipment, Plant Adjustments for Intangible Utility Plants	214		213
Plant Acquisition Adjustments [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	40
Finite-Lived Intangible Assets, Useful Life, Maximum	46
Finite-Lived Intangible Assets, Accumulated Amortization	22		16
Public Utilities, Property, Plant and Equipment, Plant Adjustments for Intangible Utility Plants	214	[1]	213	[1]
Leasehold Improvements [Member]
Finite-Lived Intangible Assets, Accumulated Amortization	9	[2]	9	[2]
Leasehold Improvements, Gross	11	[2]	13	[2]
Leasehold Improvements [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Accumulated Amortization	9	[2]	9	[2]
Leasehold Improvements, Gross	11	[1],[2]	13	[1],[2]
Rights of Way [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	50
Finite-Lived Intangible Assets, Useful Life, Maximum	75
Finite-Lived Intangible Assets, Accumulated Amortization	38		37
Finite-Lived Contractual Rights, Gross	128		140
Rights of Way [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	50
Finite-Lived Intangible Assets, Useful Life, Maximum	75
Finite-Lived Intangible Assets, Accumulated Amortization	38		37
Finite-Lived Contractual Rights, Gross	128	[1]	140	[1]
Franchises and Consents [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	5
Finite-Lived Intangible Assets, Useful Life, Maximum	30
Finite-Lived Intangible Assets, Accumulated Amortization	7		6
Finite-Lived Franchise Rights, Gross	15		15
Franchises and Consents [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Useful Life, Minimum	5
Finite-Lived Intangible Assets, Useful Life, Maximum	30
Finite-Lived Intangible Assets, Accumulated Amortization	7		6
Finite-Lived Franchise Rights, Gross	15	[1]	15	[1]
Other Intangibles [Member]
Finite-Lived Intangible Assets, Accumulated Amortization	14		14
Other Finite-Lived Intangible Assets, Gross	19		20
Other Intangibles [Member] | Consumers Energy Company [Member]
Finite-Lived Intangible Assets, Accumulated Amortization	14		14
Other Finite-Lived Intangible Assets, Gross	$ 18	[1]	$ 18	[1]

[1] Net intangible asset additions for Consumers' utility plant were $23 million during 2011 and $25 million during 2010.

[2] Leasehold improvements are amortized over the life of the lease, which may change whenever the lease is renewed or extended.