Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
DB Pension Plans and DB SERP
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 53	$ 50	$ 41
Interest cost	63	83	103
Settlement loss	1	1	0
Expected return on plan assets	(208)	(191)	(162)
Amortization of
Net loss	100	95	50
Prior service cost (credit)	4	1	1
Settlement loss	6	2	0
Net periodic cost (credit)	19	41	33
DB Pension Plans and DB SERP | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	51	49	40
Interest cost	59	78	97
Expected return on plan assets	(197)	(181)	(153)
Amortization of
Net loss	96	90	47
Prior service cost (credit)	4	1	1
Settlement loss	6	2	0
Net periodic cost (credit)	19	39	32
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	18	16	14
Interest cost	23	33	41
Settlement loss	0	0	0
Expected return on plan assets	(109)	(100)	(88)
Amortization of
Net loss	8	15	26
Prior service cost (credit)	(53)	(56)	(62)
Settlement loss	0	0	0
Net periodic cost (credit)	(113)	(92)	(69)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	17	15	13
Interest cost	23	31	40
Expected return on plan assets	(102)	(93)	(82)
Amortization of
Net loss	8	15	26
Prior service cost (credit)	(51)	(54)	(61)
Settlement loss	0	0	0
Net periodic cost (credit)	$ (105)	$ (86)	$ (64)