Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
DB Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		$ 2,512	$ 2,780
Service cost		41	48
Interest cost		98	90
Plan amendments		0	0
Actuarial loss (gain)		476	(258)
Benefits paid		(154)	(148)
Benefit obligation at end of period		2,973	2,512	$ 2,780
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		2,247	2,305
Actual return on plan assets		453	(150)
Company contribution		0	240
Actual benefits paid		(154)	(148)
Plan assets at fair value at end of period		2,546	2,247	2,305
Funded status		(427)	(265)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Funded status		(408)	(246)
DB SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		140	154
Service cost		0	0
Interest cost		5	5
Plan amendments		0	0
Actuarial loss (gain)		15	(10)
Benefits paid		(10)	(9)
Benefit obligation at end of period		150	140	154
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	9
Actual benefits paid		(10)	(9)
Plan assets at fair value at end of period		0	0	0
Funded status		(150)	(140)
DB SERP | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		101	112
Service cost		0	0
Interest cost		4	4
Plan amendments		0	0
Actuarial loss (gain)		11	(8)
Benefits paid		(7)	(7)
Benefit obligation at end of period		109	101	112
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		(109)	(101)
OPEB Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,045	1,097
Service cost		14	17	19
Interest cost		41	34	51
Plan amendments	$ 26	0
Actuarial loss (gain)		110	(74)
Benefits paid		(45)	(55)
Benefit obligation at end of period		1,165	1,045	1,097
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		1,280	1,420
Actual return on plan assets		273	(86)
Company contribution		0	0
Actual benefits paid		(44)	(54)
Plan assets at fair value at end of period		1,509	1,280	1,420
Funded status		344	235
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,004	1,053
Service cost		13	16	19
Interest cost		40	33	49
Plan amendments		0	25
Actuarial loss (gain)		106	(70)
Benefits paid		(43)	(53)
Benefit obligation at end of period		1,120	1,004	1,053
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		1,197	1,329
Actual return on plan assets		255	(80)
Company contribution		0	0
Actual benefits paid		(42)	(52)
Plan assets at fair value at end of period		1,410	1,197	$ 1,329
Funded status		$ 290	$ 193