Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
DB Pension Plans and DB SERP
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 41	$ 48	$ 45
Interest cost	103	95	93
Expected return on plan assets	(162)	(149)	(153)
Amortization of
Net loss	50	76	82
Prior service cost (credit)	1	3	5
Net periodic cost (credit)	33	73	72
DB Pension Plans and DB SERP | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	40	47	44
Interest cost	97	88	90
Expected return on plan assets	(153)	(139)	(149)
Amortization of
Net loss	47	73	79
Prior service cost (credit)	1	3	4
Net periodic cost (credit)	32	72	68
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	14	17	19
Interest cost	41	34	51
Expected return on plan assets	(88)	(97)	(90)
Amortization of
Net loss	26	15	29
Prior service cost (credit)	(62)	(67)	(40)
Net periodic cost (credit)	(69)	(98)	(31)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	13	16	19
Interest cost	40	33	49
Expected return on plan assets	(82)	(91)	(84)
Amortization of
Net loss	26	16	29
Prior service cost (credit)	(61)	(65)	(39)
Net periodic cost (credit)	$ (64)	$ (91)	$ (26)