Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) site	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($)	Nov. 30, 2014 USD ($)
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant				$ 69
Accrued rate refunds		$ 26	$ 6
Cost of gas sold		961	1,493	1,228
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Income tax benefits returned to customers		$ 64
Proceeds from government grant				69
Number of units planned to be retired | site		10
Accrued rate refunds		$ 26	6
Cost of gas sold		$ 939	1,375	1,187
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units planned to be retired | site		7
Gas-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units retired | site		3
Electric Utility [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Income tax benefits, to be returned to customers		$ 209
Tax benefit, distribution to customers, term		5 years
Gas Utility [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Income tax benefits, to be returned to customers		$ 260
Tax benefit, distribution to customers, term		12 years
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
Annual rate increase authorized		$ 165
Rate of return on equity authorized		10.30%
Depreciation Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested			$ 28
Annual rate increase authorized		$ 6
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%
Gas Cost Recover (GCR) [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Over (under) recovery requested		$ 9	(84)
Accrued rate refunds		18
Cost of gas sold		800	900
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Over (under) recovery requested		6	10
Accrued rate refunds		8
PSCR Cost of Power Sold		2,100	$ 1,900
Energy Optimization [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery/collection					$ 17
Requested recovery/collection		$ 18
Major Maintenance [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery, collection period		6 months
Authorized recovery/collection						$ 10
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery, collection period		10 years
Number of former MGPs | site		23
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery, collection period		5 years
Scenario, Forecast [Member] | Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Change in annual rate increase authorized	$ 39
Annual rate increase authorized	$ 126
Renewable Energy Grant [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant				$ 69