Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
DB Pension Plans
Net periodic cost (credit)
Service cost	$ 11	$ 12	$ 31	$ 36
Interest cost	24	22	73	67
Expected return on plan assets	(40)	(38)	(121)	(112)
Amortization of:
Net loss	12	19	36	56
Prior service cost (credit)	0	1	1	2
Net periodic cost (credit)	7	16	20	49
DB Pension Plans | Consumers Energy Company
Net periodic cost (credit)
Service cost	10	12	30	35
Interest cost	23	22	69	64
Expected return on plan assets	(38)	(35)	(114)	(104)
Amortization of:
Net loss	12	17	35	53
Prior service cost (credit)	0	1	1	2
Net periodic cost (credit)	7	17	21	50
OPEB Plan
Net periodic cost (credit)
Service cost	3	4	10	13
Interest cost	11	9	31	27
Expected return on plan assets	(22)	(24)	(66)	(73)
Amortization of:
Net loss	7	3	20	11
Prior service cost (credit)	(16)	(16)	(47)	(50)
Net periodic cost (credit)	(17)	(24)	(52)	(72)
OPEB Plan | Consumers Energy Company
Net periodic cost (credit)
Service cost	3	4	10	12
Interest cost	10	8	30	25
Expected return on plan assets	(21)	(22)	(62)	(68)
Amortization of:
Net loss	7	4	20	12
Prior service cost (credit)	(15)	(17)	(46)	(49)
Net periodic cost (credit)	$ (16)	$ (23)	$ (48)	$ (68)