Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
DB Pension Plans
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 6	$ 7
Interest cost	27	26
Expected return on plan assets	(57)	(59)
Amortization of:
Net loss	3	3
Prior service cost (credit)	1	1
Settlement loss	3	3
Net periodic credit	(17)	(19)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	6	7
Interest cost	26	24
Expected return on plan assets	(54)	(55)
Amortization of:
Net loss	2	3
Prior service cost (credit)	1	1
Settlement loss	3	3
Net periodic credit	(16)	(17)
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	2	3
Interest cost	11	11
Expected return on plan assets	(28)	(29)
Amortization of:
Net loss	1	1
Prior service cost (credit)	(9)	(8)
Settlement loss	0	0
Net periodic credit	(23)	(22)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	2	3
Interest cost	10	10
Expected return on plan assets	(26)	(27)
Amortization of:
Net loss	1	1
Prior service cost (credit)	(8)	(7)
Settlement loss	0	0
Net periodic credit	$ (21)	$ (20)