Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
DB Pension Plans
Net periodic cost (credit)
Service cost	$ 12	$ 10
Interest cost	21	25
Expected return on plan assets	(48)	(40)
Amortization of:
Net loss	22	12
Prior service credit	0	0
Net periodic cost (credit)	7	7
DB Pension Plans | Consumers Energy Company
Net periodic cost (credit)
Service cost	12	10
Interest cost	20	23
Expected return on plan assets	(45)	(38)
Amortization of:
Net loss	21	12
Prior service credit	0	0
Net periodic cost (credit)	8	7
OPEB Plan
Net periodic cost (credit)
Service cost	4	4
Interest cost	8	10
Expected return on plan assets	(25)	(22)
Amortization of:
Net loss	4	7
Prior service credit	(14)	(16)
Net periodic cost (credit)	(23)	(17)
OPEB Plan | Consumers Energy Company
Net periodic cost (credit)
Service cost	4	3
Interest cost	8	10
Expected return on plan assets	(23)	(21)
Amortization of:
Net loss	4	7
Prior service credit	(14)	(15)
Net periodic cost (credit)	$ (21)	$ (16)