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, 2018	Dec. 31, 2017	Dec. 31, 2016
DB Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		$ 2,780	$ 2,562
Service cost		48	45
Interest cost		90	88
Plan amendments		0	0
Actuarial (gain) loss		(258)	241
Benefits paid		(148)	(156)
Benefit obligation at end of period		2,512	2,780	$ 2,562
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		2,305	2,101
Actual return on plan assets		(150)	360
Company contribution		240	0
Actual benefits paid		(148)	(156)
Plan assets at fair value at end of period		2,247	2,305	2,101
Funded status		(265)	(475)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Funded status		(246)	(455)
DB SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		154	151
Service cost		0	0
Interest cost		5	5
Plan amendments		0	0
Actuarial (gain) loss		(10)	7
Benefits paid		(9)	(9)
Benefit obligation at end of period		140	154	151
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		9	9
Actual benefits paid		(9)	(9)
Plan assets at fair value at end of period		0	0	0
Funded status		(140)	(154)
DB SERP | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		112	109
Service cost		0	0
Interest cost		4	4
Plan amendments		0	0
Actuarial (gain) loss		(8)	5
Benefits paid		(7)	(6)
Benefit obligation at end of period		101	112	109
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	6
Actual benefits paid		(7)	(6)
Plan assets at fair value at end of period		0	0	0
Funded status		(101)	(112)
OPEB Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,097	1,408
Service cost		17	19	18
Interest cost		34	51	46
Plan amendments	$ 26		(309)
Actuarial (gain) loss		(74)	(24)
Benefits paid		(55)	(48)
Benefit obligation at end of period		1,045	1,097	1,408
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		1,420	1,264
Actual return on plan assets		(86)	203
Company contribution		0	0
Actual benefits paid		(54)	(47)
Plan assets at fair value at end of period		1,280	1,420	1,264
Funded status		235	323
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		1,053	1,365
Service cost		16	19	17
Interest cost		33	49	45
Plan amendments		25	(303)
Actuarial (gain) loss		(70)	(31)
Benefits paid		(53)	(46)
Benefit obligation at end of period		1,004	1,053	1,365
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period		1,329	1,184
Actual return on plan assets		(80)	190
Company contribution		0	0
Actual benefits paid		(52)	(45)
Plan assets at fair value at end of period		1,197	1,329	$ 1,184
Funded status		$ 193	$ 276