Regulatory Matters (Schedule of Components of the Annual Rate Increase Requested) (Details) - Electric Rate Case [Member] - Consumers Energy Company [Member] $ in Millions	1 Months Ended
	Sep. 30, 2017 USD ($)
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	$ 148
Investment In Rate Base [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	45
Operating And Maintenance Costs [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	42
Gross Margin [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	42
Cost Of Capital [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	28
Working Capital [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested, amended	$ (9)