Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
DB Pension Plans
Net periodic cost (credit)
Service cost	$ 10	$ 12	$ 20	$ 24
Interest cost	24	23	49	45
Expected return on plan assets	(41)	(37)	(81)	(74)
Amortization of:
Net loss	12	19	24	37
Prior service cost (credit)	1	0	1	1
Net periodic cost (credit)	6	17	13	33
DB Pension Plans | Consumers Energy Company
Net periodic cost (credit)
Service cost	10	11	20	23
Interest cost	23	21	46	42
Expected return on plan assets	(38)	(34)	(76)	(69)
Amortization of:
Net loss	11	18	23	36
Prior service cost (credit)	1	0	1	1
Net periodic cost (credit)	7	16	14	33
OPEB Plan
Net periodic cost (credit)
Service cost	3	5	7	9
Interest cost	10	9	20	18
Expected return on plan assets	(22)	(25)	(44)	(49)
Amortization of:
Net loss	6	4	13	8
Prior service cost (credit)	(15)	(17)	(31)	(34)
Net periodic cost (credit)	(18)	(24)	(35)	(48)
OPEB Plan | Consumers Energy Company
Net periodic cost (credit)
Service cost	4	4	7	8
Interest cost	10	9	20	17
Expected return on plan assets	(20)	(23)	(41)	(46)
Amortization of:
Net loss	6	4	13	8
Prior service cost (credit)	(16)	(16)	(31)	(32)
Net periodic cost (credit)	$ (16)	$ (22)	$ (32)	$ (45)