Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
DB Pension Plans
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 13	$ 13	$ 27	$ 25
Interest cost	15	20	30	41
Expected return on plan assets	(52)	(48)	(104)	(96)
Amortization of
Net loss	26	22	51	44
Prior service cost (credit)	1	1	2	1
Settlement loss	2	0	3	0
Net periodic cost (credit)	5	8	9	15
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	13	12	26	24
Interest cost	14	19	28	39
Expected return on plan assets	(49)	(46)	(98)	(91)
Amortization of
Net loss	24	21	49	42
Prior service cost (credit)	1	1	2	1
Settlement loss	2	0	3	0
Net periodic cost (credit)	5	7	10	15
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	5	4	9	8
Interest cost	5	9	11	17
Expected return on plan assets	(27)	(25)	(54)	(50)
Amortization of
Net loss	2	3	4	7
Prior service cost (credit)	(13)	(14)	(26)	(28)
Settlement loss	0	0	0	0
Net periodic cost (credit)	(28)	(23)	(56)	(46)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	5	4	9	8
Interest cost	5	8	11	16
Expected return on plan assets	(26)	(24)	(51)	(47)
Amortization of
Net loss	2	3	4	7
Prior service cost (credit)	(13)	(13)	(26)	(27)
Settlement loss	0	0	0	0
Net periodic cost (credit)	$ (27)	$ (22)	$ (53)	$ (43)