Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended							3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Oct. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Aug. 31, 2019 USD ($)	May 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current	$ 72							$ 72		$ 72		$ 155
Regulatory liabilities, noncurrent	3,754							3,754		3,754		3,681
Regulatory assets	2,367							2,367		2,367		1,743
Revenue								1,546	$ 1,599	5,050	$ 5,044
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current	72							72		72		155
Regulatory liabilities, noncurrent	3,754							3,754		3,754		3,681
Regulatory assets	2,367							2,367		2,367		1,743
Revenue								1,429	$ 1,502	4,706	$ 4,752
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	62							62		62
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase (decrease) 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													$ 34
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase (decrease) 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
Approved interim bill credit	32
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 (decrease) authorized			$ 89
Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase (decrease) authorized	$ 144
Rate of return on equity authorized	9.90%
Annual rate increase requested				$ 229
Rate of return on equity requested				10.75%
Annual rate increase requested, amended		$ 204
Gas Rate TCJA Adjustment | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase (decrease) authorized	$ (13)
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
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]
Regulatory assets	$ 657							$ 657		$ 657
Number of units | coal_fueled_electric_generating_unit	2							2		2