Plant, Property, and Equipment (Schedule of Finite Lived Intangible Assets Amortization Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Public Utility, Property, Plant and Equipment [Line Items]
Amortization of Intangible Assets	$ 59	$ 48	$ 39
Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Amortization of Intangible Assets	58	47	38
Software and Software Development Costs [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Amortization of Intangible Assets	50	39	31
Software and Software Development Costs [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Amortization of Intangible Assets	49	39	30
Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	70
Minimum [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	70
Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	105
Maximum [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	$ 105