Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended								3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($)	Apr. 30, 2016 USD ($) item	Mar. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Nov. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	$ 80								$ 80		$ 80		$ 82
Operating Revenue									1,587	$ 1,486	4,759	$ 4,947
Accrued rate refunds	33								33		33		26
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	80								80		80		82
Operating Revenue									1,498	$ 1,417	4,514	$ 4,726
Accrued rate refunds	33								33		33		26
Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Change in net plant, property, and equipment		$ 34
2014 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested								$ 163
Annual rate increase self-implemented							$ 110
Annual rate increase authorized		$ 126
Rate of return on equity authorized					10.30%
Temporary rate increase					$ 165
Number of units retired | item		7
2014 Electric Rate Case [Member] | Self-Implemented Rate Refunds [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current														$ 1
2016 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested			$ 225
Rate of return on equity requested			10.70%
Investment recovery, 2017			$ 38
Investment recovery, 2018			92
Investment recovery, 2019			$ 92
Annual rate increase self-implemented	170
Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested						$ 85
Rate of return on equity requested						10.70%
Annual rate increase self-implemented				$ 60
Annual rate increase authorized		$ 40
Gas Rate Case [Member] | Self-Implemented Rate Refunds [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current	10								10		10
Energy Optimization Plan Incentive [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Operating Revenue													$ 18
Authorized recovery/collection	$ 18								$ 18		18
Current FERC Revenue Requirement [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Revenue requirement											9
METC Proposed FERC Revenue Requirement [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Revenue requirement											6
2016 PSCR [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Litigation costs											$ 6