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, 2016 USD ($)
DB Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ 82
AOCI	2
DB Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	82
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	(2)
AOCI	(2)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ (2)