Retirement Benefits (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
DB Pension Plans and DB SERP
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	$ 29	$ 41	$ 53
Interest cost	112	84	63
Settlement loss	0	1	1
Expected return on plan assets	(220)	(206)	(208)
Amortization of:
Net loss	12	40	100
Prior service cost (credit)	4	4	4
Settlement loss	11	9	6
Net periodic cost (credit)	(52)	(27)	19
DB Pension Plans and DB SERP | Volatility Mechanism
Amortization of:
Deferred costs (credits)	(11)
DB Pension Plans and DB SERP | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	28	39	51
Interest cost	105	79	59
Expected return on plan assets	(208)	(194)	(197)
Amortization of:
Net loss	11	37	96
Prior service cost (credit)	4	4	4
Settlement loss	11	9	6
Net periodic cost (credit)	(49)	(26)	19
OPEB Plan
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	12	17	18
Interest cost	44	28	23
Settlement loss	0	0	0
Expected return on plan assets	(103)	(115)	(109)
Amortization of:
Net loss	12	1	8
Prior service cost (credit)	(41)	(51)	(53)
Settlement loss	0	0	0
Net periodic cost (credit)	(76)	(120)	(113)
OPEB Plan | Volatility Mechanism
Amortization of:
Deferred costs (credits)	23
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Service cost	11	17	17
Interest cost	42	27	23
Expected return on plan assets	(95)	(107)	(102)
Amortization of:
Net loss	12	0	8
Prior service cost (credit)	(40)	(50)	(51)
Settlement loss	0	0	0
Net periodic cost (credit)	$ (70)	$ (113)	$ (105)