Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
DB Pension Plans and DB SERP
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 48	$ 45	$ 42
Interest cost	95	93	90
Expected return on plan assets	(149)	(153)	(147)
Amortization of
Net loss	76	82	71
Prior service cost (credit)	3	5	4
Net periodic cost (credit)	73	72	60
DB Pension Plans and DB SERP | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	47	44	41
Interest cost	88	90	87
Expected return on plan assets	(139)	(149)	(143)
Amortization of
Net loss	73	79	68
Prior service cost (credit)	3	4	4
Net periodic cost (credit)	72	68	57
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	17	19	18
Interest cost	34	51	46
Expected return on plan assets	(97)	(90)	(85)
Amortization of
Net loss	15	29	21
Prior service cost (credit)	(67)	(40)	(41)
Net periodic cost (credit)	(98)	(31)	(41)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	16	19	17
Interest cost	33	49	45
Expected return on plan assets	(91)	(84)	(80)
Amortization of
Net loss	16	29	22
Prior service cost (credit)	(65)	(39)	(40)
Net periodic cost (credit)	$ (91)	$ (26)	$ (36)