Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended												3 Months Ended								12 Months Ended
	Jul. 31, 2020 USD ($)	Jul. 31, 2019 USD ($)	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Aug. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) site	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) site	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) site	Dec. 31, 2015 site	Dec. 31, 2013 USD ($)	Dec. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)
Public Utilities, General Disclosures [Line Items]
Revenue													$ 1,829	$ 1,599	$ 1,492	$ 1,953	$ 1,778	$ 1,527	$ 1,449	$ 1,829	$ 6,873	$ 6,583	$ 6,399
Regulatory liabilities, current													155				80				155	80
Regulatory liability, noncurrent													3,681				3,715				3,681	3,715
Regulatory assets, noncurrent													1,743				1,764				1,743	1,764
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Revenue													1,712	$ 1,502	1,395	1,855	1,686	$ 1,437	$ 1,362	$ 1,737	$ 6,464	6,222	6,064
Number of units retired | site																					10
Regulatory liabilities, current													155				80				$ 155	80
Regulatory liability, noncurrent													3,681				3,715				3,681	3,715
Regulatory assets, noncurrent													1,743				1,764				1,743	1,764
Purchased and interchange power																					1,587	1,491	1,486
Cost of gas sold																					819	730	$ 693
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													31								31
Revenue																					$ 34	31
Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized							$ (49)
Annual rate increase requested, amended									$ 83
Gas Rate Case Net Of TCJA Impact | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized					$ 60
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized						$ (113)
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized							72		$ 66
Annual rate increase requested								$ 58				$ 173
Rate of return on equity requested								10.75%				10.50%
Annual rate increase requested, amended				$ 44							$ 148
Annual rate increase self-implemented										$ 130
Rate of return on equity authorized									10.00%
Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized					$ 11
Annual rate increase requested										$ 178
Rate of return on equity requested										10.50%
Annual rate increase requested, amended						$ 60			$ 145
Amended requested rate change						10.00%			10.75%
Rate of return on equity authorized					10.00%
PSCR overrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Purchased and interchange power							1,900		$ 1,900
Over (under) recovery authorized by the MPSC							12		$ 32						12	$ 32
GCR overrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Over (under) recovery authorized by the MPSC							1	$ 2							$ 1
Cost of gas sold							$ 600	$ 500
Manufactured Gas Plant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent																	142					142
Gas Storage Inventory Adjustments | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period																					5 years
Regulatory assets, noncurrent													4				10				$ 4	10
Scenario, Forecast | Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection																										$ 34
Scenario, Forecast | Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ 10	$ 9
Renewable energy grant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Proceeds from government grant																									$ 69
Regulatory liability, noncurrent													54				56				54	56
Revenue subject to refund tax reform rate change | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current																											$ 31
Revenue subject to refund tax reform rate change | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current													70								70
Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent																	$ 1,600					$ 1,600
Income Taxes, Net | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent				400
Income Taxes, Net | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent				1,200
Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent				$ 1,700
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
Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent				$ 300
Income Taxes Not Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period				44 years
Income Taxes Not Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period				27 years
Taxes Not Related To Plant Assets | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent				$ 200
Regulatory liability remaining book life				15 years
Revenue Subject To Refund Other | Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current													$ 36								$ 36
Manufactured Gas Plant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of former MGPs | site													23								23
Regulatory asset collection period																					10 years
Regulatory assets, noncurrent													$ 133								$ 133
Subsequent Event | Electric Rate Case Net Of TCJA Impact | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized			$ 89
Subsequent Event | Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized			$ (24)
Rate of return on equity authorized			10.00%