Plant, Property, and Equipment (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Property, Plant and Equipment [Line Items]
Payments to acquire plant	$ 1,564	$ 1,577	$ 1,325
Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Payments to acquire plant	$ 1,537	$ 1,573	$ 1,320
Gas Fueled Electric Generating Units [Member] | Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Plant capacity | MW	540
Payments to acquire plant	$ 155
Goodwill	0
Minimum [Member]
Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	84
Minimum [Member] | Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	84
Maximum [Member]
Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	110
Maximum [Member] | Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Expected future amortization expense of intangible assets, per year	$ 110