Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
DB Pension Plans
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 7	$ 7
Interest cost	26	27
Expected return on plan assets	(59)	(55)
Amortization of:
Net loss	3	3
Prior service cost (credit)	1	1
Settlement loss	3	2
Net periodic credit	(19)	(15)
DB Pension Plans | Volatility Mechanism
Amortization of:
Deferred costs (credits)	(5)
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	7	7
Interest cost	24	25
Expected return on plan assets	(55)	(52)
Amortization of:
Net loss	3	3
Prior service cost (credit)	1	1
Settlement loss	3	2
Net periodic credit	(17)	(14)
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	3	3
Interest cost	11	11
Expected return on plan assets	(29)	(26)
Amortization of:
Net loss	1	3
Prior service cost (credit)	(8)	(10)
Settlement loss	0	0
Net periodic credit	(22)	(19)
OPEB Plan | Volatility Mechanism
Amortization of:
Deferred costs (credits)	1
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	3	3
Interest cost	10	11
Expected return on plan assets	(27)	(24)
Amortization of:
Net loss	1	3
Prior service cost (credit)	(7)	(10)
Settlement loss	0	0
Net periodic credit	$ (20)	$ (17)