Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended					3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Jan. 31, 2015	Dec. 31, 2014	Jul. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Operating Revenue						$ 1,486	$ 1,430	$ 4,947	$ 5,421
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Operating Revenue						$ 1,417	$ 1,359	$ 4,726	$ 5,128
Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested				$ 163
Rate of return on equity requested				10.70%
Annual rate increase self-implemented		$ 110
Electric Rate Case [Member] | Consumers Energy Company [Member] | 2016 and 2017 Planned Investments [Member]
Public Utilities, General Disclosures [Line Items]
Investment recovery mechanism requested				$ 163
Electric Rate Case [Member] | Consumers Energy Company [Member] | 2018 Planned Investments [Member]
Public Utilities, General Disclosures [Line Items]
Investment recovery mechanism requested				$ 78
Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested					$ 88
Annual rate increase authorized			$ 45
Rate of return on equity authorized			10.30%
Energy Optimization Plan Incentive [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ 17
Operating Revenue										$ 17