Regulatory Matters (Narrative) (Details) $ in Millions		1 Months Ended												3 Months Ended								12 Months Ended
		Jan. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Jan. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Aug. 31, 2016 USD ($)	Apr. 30, 2016 site	Mar. 31, 2016 USD ($)	Jun. 30, 2015 site	Dec. 31, 2017 USD ($) site	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($) site	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)
Public Utilities, General Disclosures [Line Items]
U.S. federal income tax rate																							35.00%
Increase (decrease) to deferred tax liabilities related to tax rate changes																							$ 1,300
Revenue														$ 1,778	$ 1,527	$ 1,449	$ 1,829	$ 1,640	$ 1,587	$ 1,371	$ 1,801		6,583		$ 6,399		$ 6,456
Regulatory liability current														80				95					80		95
Accrued rate refunds														33				21					33		21
Cost of gas sold																							750		710		961
Asset Retirement Obligation														430				447					430		447		439
ARO removed																							45		18
Regulatory assets, noncurrent														1,764				2,091					1,764		2,091
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities														3,795				2,136					3,795		2,136
Revenue														1,686	1,437	$ 1,362	1,737	1,550	$ 1,498	$ 1,293	1,723		6,222		6,064		6,165
Regulatory liability current														80				95					$ 80		95
Number of units retired | site																							10
Accrued rate refunds														33				21					$ 33		21
Cost of gas sold																							730		693		939
Property, plant and equipment	[1]													16,630				15,603					16,630		15,603
Asset Retirement Obligation														429				446					429		446		438
ARO removed																							45		18
Regulatory assets, noncurrent														1,764				2,091					1,764		2,091
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units retired | site											7
Cost of unit decommissioning														63
Property, plant and equipment														0									0
Decommissioning liability			$ 63
ARO removed														16
Gas-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Number of units retired | site													3
Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested						$ 173						$ 225
Rate of return on equity requested						10.50%						10.70%
Annual rate increase requested, amended				$ 148
Annual rate increase self-implemented			$ 130						$ 170
Self-implemented rate increase collected																							32
Annual rate increase authorized							$ 113
Rate of return on equity authorized							10.10%
Electric Rate Case [Member] | Consumers Energy Company [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Recommended annual rate increase		$ 30
Depreciation Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized						$ (3)
FERC Transmission Order [Member] | Electric Transmission [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Rate of return on equity authorized									10.32%	12.38%
Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested										$ 90
Rate of return on equity requested										10.60%
Annual rate increase requested, amended						80
Annual rate increase self-implemented								$ 20
Annual rate increase authorized					$ 29
Rate of return on equity authorized					10.10%
Investment recovery approved, 2019					$ 18
Investment recovery approved, 2018					$ 18
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														6				13					6		13
Over (under) recovery authorized by the MPSC												$ 2									$ 2					$ 2
Cost of gas sold																								$ 500		$ 500
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Over (under) recovery requested																		(9)							(9)		6
Over (under) recovery amended requested																											12
Accrued rate refunds														27				8					27		8
PSCR Cost of Power Sold																									1,900		1,900
Over (under) recovery authorized by the MPSC																											$ 21
Power Supply Cost Recover (PSCR) [Member] | Electric Transmission [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Accrued rate refunds							$ 28
Energy Waste Reduction Plan [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery/collection				18											18
Revenue																							31		18
Requested recovery/collection														$ 31									$ 31
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
Regulatory assets, noncurrent														$ 142				139					$ 142		139
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Authorized recovery, collection period																							5 years
Regulatory assets, noncurrent	[2]													10				14					$ 10		14
ARO [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent	[3]													161				166					161		166
ARO [Member] | Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent				$ 16											$ 16
Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
U.S. federal income tax rate																						21.00%
Renewable Energy Grant [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant																												$ 69
Revenue Subject To Refund [Member] | Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current																		$ 17							$ 17
Net Regulatory Tax Liability [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities														$ 1,588									$ 1,588

[1] For the year ended December 31, 2017, Consumers' plant additions were $1.7 billion and plant retirements were $214 million. For the year ended December 31, 2016, Consumers' plant additions were $2.3 billion and plant retirements were $285 million.

[2] These regulatory assets represent incurred costs for which the MPSC has provided, or Consumers expects, recovery without a return on investment.

[3] The MPSC has authorized a specific return on this regulatory asset.