Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended									3 Months Ended								12 Months Ended
	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Apr. 30, 2016 USD ($) item site	Mar. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Nov. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 USD ($) site	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) site	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) site	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Public Utilities, General Disclosures [Line Items]
Revenue										$ 1,640	$ 1,587	$ 1,371	$ 1,801	$ 1,509	$ 1,486	$ 1,350	$ 2,111	$ 6,399		$ 6,456		$ 7,179
Regulatory liability current										95				82				95		82
Accrued rate refunds										21				26				21		26
Cost of gas sold																		710		961		1,493
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Income tax benefits returned to customers																		64
Revenue										1,550	1,498	1,293	1,723	1,439	$ 1,417	$ 1,281	2,028	6,064		6,165		6,800
Regulatory liability current										95				82				$ 95		82
Number of units retired | site																		10
Accrued rate refunds										21				26				$ 21		26
Cost of gas sold																		693		939		1,375
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units 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
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 Cost Recover (GCR) [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Over (under) recovery requested				$ 2									$ 2						$ 2
Accrued rate refunds										13				18				$ 13		18
Over (under) recovery authorized by the MPSC																	$ 9				$ 9		$ (84)
Cost of gas sold																			$ 500		$ 800		$ 900
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Over (under) recovery requested														6						6
Litigation costs																		6
Accrued rate refunds										8				8				8		8
PSCR Cost of Power Sold																				1,900		2,100		$ 1,900
Over (under) recovery authorized by the MPSC									$ 5													$ 5		9
Energy Optimization [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery/collection		$ 18									$ 18
Revenue																		18		18
Requested recovery/collection										$ 18								$ 18
2014 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units retired | item			7
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
2016 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Amended Annual Rate Increase Request	$ 208
Annual rate increase requested				$ 225
Rate of return on equity requested				10.70%
Annual rate increase self-implemented		$ 170
Investment recovery, 2017				$ 38
Investment recovery, 2018				92
Investment recovery, 2019				$ 92
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								23
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery, collection period																		5 years
Renewable Energy Grant [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant																								$ 69
Revenue Subject To Refund [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current										$ 31				18				$ 31		18
Revenue Subject To Refund [Member] | Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current										$ 10								$ 10
Revenue Subject To Refund [Member] | 2014 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current												$ 1
Revenue Subject To Refund [Member] | Securitized Costs [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current														$ 14						$ 14