Retirement Benefits (Schedule Of Net Loss And Prior Service Cost (Credit) That Will Be Amortized In Next Fiscal Year) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ 47
AOCI	3
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	47
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	(35)
AOCI	(1)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ (35)