Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
DB Pension Plans and DB SERP
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 28	$ 29	$ 41
Interest cost	109	112	84
Settlement loss	0	0	1
Expected return on plan assets	(234)	(220)	(206)
Amortization of:
Net loss	12	12	40
Prior service cost (credit)	4	4	4
Settlement loss	11	11	9
Net periodic credit	(70)	(52)	(27)
DB Pension Plans and DB SERP | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	27	28	39
Interest cost	102	105	79
Expected return on plan assets	(221)	(208)	(194)
Amortization of:
Net loss	11	11	37
Prior service cost (credit)	4	4	4
Settlement loss	11	11	9
Net periodic credit	(66)	(49)	(26)
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	11	12	17
Interest cost	43	44	28
Settlement loss	0	0	0
Expected return on plan assets	(115)	(103)	(115)
Amortization of:
Net loss	4	12	1
Prior service cost (credit)	(31)	(41)	(51)
Settlement loss	0	0	0
Net periodic credit	(88)	(76)	(120)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	11	11	17
Interest cost	41	42	27
Expected return on plan assets	(107)	(95)	(107)
Amortization of:
Net loss	4	12	0
Prior service cost (credit)	(30)	(40)	(50)
Settlement loss	0	0	0
Net periodic credit	$ (81)	$ (70)	$ (113)