Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
DB Pension Plans
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 14	$ 12	$ 41	$ 37
Interest cost	14	20	44	61
Settlement loss	0	(1)	0	(1)
Expected return on plan assets	(51)	(47)	(155)	(143)
Amortization of
Net loss	25	23	76	67
Prior service cost (credit)	1	0	3	1
Settlement loss	1	0	4	0
Net periodic cost (credit)	4	9	13	24
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	14	12	40	36
Interest cost	14	20	42	59
Expected return on plan assets	(49)	(45)	(147)	(136)
Amortization of
Net loss	24	22	73	64
Prior service cost (credit)	1	0	3	1
Settlement loss	1	0	4	0
Net periodic cost (credit)	5	9	15	24
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	5	4	14	12
Interest cost	6	8	17	25
Settlement loss	0	0	0	0
Expected return on plan assets	(28)	(25)	(82)	(75)
Amortization of
Net loss	2	4	6	11
Prior service cost (credit)	(14)	(14)	(40)	(42)
Settlement loss	0	0	0	0
Net periodic cost (credit)	(29)	(23)	(85)	(69)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	4	3	13	11
Interest cost	6	8	17	24
Expected return on plan assets	(26)	(23)	(77)	(70)
Amortization of
Net loss	2	4	6	11
Prior service cost (credit)	(12)	(13)	(38)	(40)
Settlement loss	0	0	0	0
Net periodic cost (credit)	$ (26)	$ (21)	$ (79)	$ (64)