Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
DB Pension Plans
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 6	$ 7	$ 19	$ 21
Interest cost	27	26	81	78
Expected return on plan assets	(57)	(58)	(171)	(176)
Amortization of:
Net loss	3	3	8	9
Prior service cost (credit)	1	1	3	3
Settlement loss	3	3	8	8
Net periodic credit	(17)	(18)	(52)	(57)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	6	7	18	20
Interest cost	26	25	77	74
Expected return on plan assets	(54)	(56)	(162)	(166)
Amortization of:
Net loss	2	3	7	8
Prior service cost (credit)	1	1	3	3
Settlement loss	3	3	8	8
Net periodic credit	(16)	(17)	(49)	(53)
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	2	2	6	8
Interest cost	10	10	32	32
Expected return on plan assets	(27)	(28)	(83)	(86)
Amortization of:
Net loss	0	1	2	3
Prior service cost (credit)	(8)	(7)	(25)	(23)
Settlement loss	0	0	0	0
Net periodic credit	(23)	(22)	(68)	(66)
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	2	2	6	8
Interest cost	11	11	32	31
Expected return on plan assets	(26)	(26)	(78)	(80)
Amortization of:
Net loss	0	1	2	3
Prior service cost (credit)	(8)	(8)	(25)	(23)
Settlement loss	0	0	0	0
Net periodic credit	$ (21)	$ (20)	$ (63)	$ (61)