Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Jun. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	May 31, 2019 USD ($)	Nov. 30, 2018 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					$ 67		$ 67		$ 155
Regulatory liabilities, noncurrent					3,786		3,786		3,681
Regulatory assets					2,344		2,344		1,743
Revenue					1,445	$ 1,492	3,504	$ 3,445
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					67		67		155
Regulatory liabilities, noncurrent					3,786		3,786		3,681
Regulatory assets					2,344		2,344		1,743
Revenue					1,334	$ 1,395	3,277	$ 3,250
Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent		$ 1,600
Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent		1,700
Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets		300
Taxes Not Related To Plant Assets | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent		$ 200
Regulatory liability remaining life (in years)		10 years
TCJA Reserve For Refund | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent					53		53
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ (24)		$ 72
Rate of return on equity authorized	10.00%		10.00%
Annual rate increase requested				$ 58
Rate of return on equity requested				10.75%
Annual rate increase requested, amended		$ 44
Electric Rate Case | Revenue Subject to Refund - Other | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					36		36
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ (113)
Electric Rate Case Tax Reform Rate Change | Revenue Subject to Refund - Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current									70
Electric Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent		$ 1,200
Electric Rate Case Tax Reform Rate Change | Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining life (in years)		27 years
Electric Rate Case Tax Reform Rate Change | Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset remaining life (in years)		27 years
Electric Rate Case Net Of TCJA Impact | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ 89
Gas Rate Case Tax Reform Rate Change | Revenue Subject to Refund - Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current											$ 31
Gas Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent		$ 400
Gas Rate Case Tax Reform Rate Change | Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining life (in years)		44 years
Gas Rate Case Tax Reform Rate Change | Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset remaining life (in years)		44 years
Gas Rate Case And Electric Rate Case Tax Reform Rate Change | Revenue Subject to Refund - Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					$ 9		$ 9
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection										$ 34
Revenue									$ 34
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
Regulatory assets					$ 657		$ 657