Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
DB Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$ 2,973	$ 2,512
Service cost	50	41
Interest cost	79	98
Plan amendments	24	0
Actuarial loss	355	476
Benefits paid	(215)	(154)
Benefit obligation at end of period	3,266	2,973	$ 2,512
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	2,546	2,247
Actual return on plan assets	371	453
Company contribution	700	0
Actual benefits paid	(215)	(154)
Plan assets at fair value at end of period	3,402	2,546	2,247
Funded status	136	(427)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Funded status	138	(408)
DB SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	150	140
Service cost	0	0
Interest cost	4	5
Plan amendments	0	0
Actuarial loss	16	15
Benefits paid	(10)	(10)
Benefit obligation at end of period	160	150	140
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	0	0
Actual return on plan assets	0	0
Company contribution	10	10
Actual benefits paid	(10)	(10)
Plan assets at fair value at end of period	0	0	0
Funded status	(160)	(150)
DB SERP | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	109	101
Service cost	0	0
Interest cost	3	4
Actuarial loss	12	11
Benefits paid	(7)	(7)
Benefit obligation at end of period	117	109	101
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	0	0
Actual return on plan assets	0	0
Company contribution	7	7
Actual benefits paid	(7)	(7)
Plan assets at fair value at end of period	0	0	0
Funded status	(117)	(109)
OPEB Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	1,165	1,045
Service cost	16	14	17
Interest cost	33	41	34
Plan amendments	0	0
Actuarial loss	39	110
Benefits paid	(48)	(45)
Benefit obligation at end of period	1,205	1,165	1,045
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,509	1,280
Actual return on plan assets	182	273
Company contribution	1	0
Actual benefits paid	(47)	(44)
Plan assets at fair value at end of period	1,645	1,509	1,280
Funded status	440	344
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	1,120	1,004
Service cost	15	13	16
Interest cost	31	40	33
Actuarial loss	37	106
Benefits paid	(45)	(43)
Benefit obligation at end of period	1,158	1,120	1,004
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,410	1,197
Actual return on plan assets	169	255
Company contribution	1	0
Actual benefits paid	(45)	(42)
Plan assets at fair value at end of period	1,535	1,410	$ 1,197
Funded status	$ 377	$ 290