Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended		12 Months Ended
	Jan. 31, 2019	Oct. 31, 2018	Jun. 30, 2018	May 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	May 31, 2019	Nov. 30, 2018
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					$ 107		$ 155
Regulatory liabilities, noncurrent					3,736		3,681
Regulatory assets					1,711		1,743
Revenue					2,059	$ 1,953
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current					107		155
Regulatory liabilities, noncurrent					3,736		3,681
Regulatory assets					1,711		1,743
Revenue					1,943	$ 1,855
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					48
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
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					$ 49
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Revenue							$ 34
Scenario, Forecast | Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection								$ 34