Retirement Benefits (Schedule Of Net Loss And Prior Service Cost (Credit) That Will Be Amortized In 2015) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ 72
AOCI	1
Pension Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	72
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	(18)
AOCI	(2)
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ (18)