Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended						3 Months Ended								12 Months Ended							25 Months Ended
	Dec. 31, 2020 USD ($) coal_fueled_electric_generating_unit site	Sep. 30, 2020 USD ($)	Jul. 31, 2020 USD ($)	May 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) coal_fueled_electric_generating_unit site	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) coal_fueled_electric_generating_unit site	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 site	Dec. 31, 2013 USD ($)	Sep. 30, 2022 USD ($)	Nov. 30, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Revenue							$ 1,798	$ 1,575	$ 1,443	$ 1,864	$ 1,795	$ 1,546	$ 1,445	$ 2,059	$ 6,680		$ 6,845		$ 6,873
Regulatory liabilities, current	$ 151					$ 87	151				87				151		87
Income tax benefit															(133)		(147)		(115)
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Revenue							1,665	$ 1,450	$ 1,330	1,744	1,670	$ 1,429	$ 1,334	1,943	$ 6,189		6,376		6,464
Number of units retired | site															10
Regulatory liabilities, current	$ 151					87	$ 151				87				$ 151		87
Income tax benefit															(173)		(185)		(142)
Purchased and interchange power															1,454		1,470		1,587
Cost of gas sold															$ 568		754		819
Costs of coal-fueled electric generating units to be retired | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units | coal_fueled_electric_generating_unit	2						2								2
Coal-Fueled Electric Generation | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units retired | site																				7
Gas-Fueled Electric Generation | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units retired | site																				3
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Authorized recovery collection																							$ 34
Revenue															$ 42		34
Requested recovery/collection	$ 42						$ 42								42
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	(36)
Electric Rate Case Net Of TCJA Impact | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	126
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested					$ 244
Rate of return on equity requested					10.50%
Annual rate increase requested, amended			$ 230
Annual rate increase authorized	$ 90
Rate of return on equity authorized	9.90%
Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested						$ 245
Rate of return on equity requested						10.50%
Annual rate increase requested, amended				$ 229
Annual rate increase authorized		$ 144
Rate of return on equity authorized		9.90%
Gas Rate Case | Consumers Energy Company | Forecast
Public Utilities, General Disclosures [Line Items]
Income tax benefit																						$ 84
PSCR overrecoveries/underrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Purchased and interchange power																	1,900		2,000
Over (under) recovery authorized by the MPSC						$ 21					$ 21						$ 21		$ (28)
GCR underrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Over (under) recovery authorized by the MPSC										$ (1)				$ (11)		$ (1)		$ (11)
Cost of gas sold																$ 500		600
GCR underrecoveries | Consumers Energy Company | Ray Compressor Station
Public Utilities, General Disclosures [Line Items]
Cost of gas sold																		$ 7
Deferred capital spending | Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Authorized recovery collection	$ 13						13								13
Financial Compensation Mechanism PPAs | Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Authorized recovery collection	$ 3						$ 3								3
Revenue															$ 1
Renewable energy grant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant																					$ 69
Income Taxes Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining book life															44 years
Income Taxes Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining book life															27 years
Manufactured Gas Plant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of former MGPs | site	23						23								23
Regulatory asset collection period															10 years