Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
DB Pension Plans
Net periodic cost (credit)
Service cost	$ 13	$ 10	$ 25	$ 20
Interest cost	20	24	41	49
Expected return on plan assets	(48)	(41)	(96)	(81)
Amortization of:
Net loss	22	12	44	24
Prior service cost (credit)	1	1	1	1
Net periodic cost (credit)	8	6	15	13
DB Pension Plans | Consumers Energy Company
Net periodic cost (credit)
Service cost	12	10	24	20
Interest cost	19	23	39	46
Expected return on plan assets	(46)	(38)	(91)	(76)
Amortization of:
Net loss	21	11	42	23
Prior service cost (credit)	1	1	1	1
Net periodic cost (credit)	7	7	15	14
OPEB Plan
Net periodic cost (credit)
Service cost	4	3	8	7
Interest cost	9	10	17	20
Expected return on plan assets	(25)	(22)	(50)	(44)
Amortization of:
Net loss	3	6	7	13
Prior service cost (credit)	(14)	(15)	(28)	(31)
Net periodic cost (credit)	(23)	(18)	(46)	(35)
OPEB Plan | Consumers Energy Company
Net periodic cost (credit)
Service cost	4	4	8	7
Interest cost	8	10	16	20
Expected return on plan assets	(24)	(20)	(47)	(41)
Amortization of:
Net loss	3	6	7	13
Prior service cost (credit)	(13)	(16)	(27)	(31)
Net periodic cost (credit)	$ (22)	$ (16)	$ (43)	$ (32)