Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended										3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Oct. 25, 2018	Aug. 31, 2018	Jul. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Oct. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	May 31, 2018
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current											$ 165		$ 165		$ 80
Regulatory liabilities, noncurrent											3,745		3,745		3,715
Regulatory assets											1,655		1,655		1,764
Revenue											1,599	$ 1,527	5,044	$ 4,805
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current											165		165		80
Regulatory liabilities, noncurrent											3,745		3,745		3,715
Regulatory assets											1,655		1,655		1,764
Revenue											1,502	$ 1,437	4,752	$ 4,536
Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent											1,600		1,600
Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent											1,700		1,700
Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets											300		300
Taxes Not Related To Plant Assets | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent											200		200
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested										$ 173
Rate of return on equity requested										10.50%
Annual rate increase requested, amended									$ 148
Annual rate increase self-implemented								$ 130
Annual rate increase authorized						$ 72	$ 66
Rate of return on equity authorized							10.00%
Electric Rate Case | Revenue Subject to Refund - Other | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current											36		36
Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested								$ 178
Rate of return on equity requested								10.50%
Annual rate increase requested, amended					$ 60		$ 145
Annual rate increase authorized				$ 11
Rate of return on equity authorized				10.00%
Authorized amended return on equity					10.00%
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		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		1,200
Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended							$ 83
Annual rate increase authorized						$ (49)
Authorized amended return on equity							10.75%
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		31
Gas Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, noncurrent											$ 400		$ 400
Energy Waste Reduction Plan | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection																$ 31
Revenue															$ 31
Scenario, Forecast | Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ 10	$ 9
Subsequent Event | Taxes Not Related To Plant Assets | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining life (in years)			15 years
Subsequent Event | 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)			36 years
Subsequent Event | 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
Subsequent Event | 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
Subsequent Event | 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