Retirement Benefits (Schedule of Funded Status of Retirement Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
DB Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$ 2,195	$ 2,169
Service cost	28	29
Interest cost	104	106
Plan amendments	0	0
Actuarial loss (gain)	(91)	52
Benefits paid	(142)	(161)
Benefit obligation at end of period	2,094	2,195	$ 2,169
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	3,004	2,820
Actual return on plan assets	102	345
Company contribution	0	0
Actual benefits paid	(142)	(161)
Plan assets at fair value at end of period	2,964	3,004	2,820
Funded status	870	809
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Funded status	836	781
DB SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	114	117
Service cost	0	0
Interest cost	5	6
Plan amendments	0	0
Actuarial loss (gain)	(4)	1
Benefits paid	(10)	(10)
Benefit obligation at end of period	105	114	117
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	0	0
Actual return on plan assets	0	0
Company contribution	10	10
Actual benefits paid	(10)	(10)
Plan assets at fair value at end of period	0	0	0
Funded status	(105)	(114)
DB SERP | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	83	85
Service cost	0	0
Interest cost	4	4
Plan amendments	0	0
Actuarial loss (gain)	(4)	1
Benefits paid	(7)	(7)
Benefit obligation at end of period	76	83	85
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	0	0
Actual return on plan assets	0	0
Company contribution	7	7
Actual benefits paid	(7)	(7)
Plan assets at fair value at end of period	0	0	0
Funded status	(76)	(83)
OPEB Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	900	889
Service cost	11	12	17
Interest cost	43	44	28
Plan amendments	(25)	0
Actuarial loss (gain)	(40)	9
Benefits paid	(58)	(54)
Benefit obligation at end of period	831	900	889
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,559	1,446
Actual return on plan assets	86	165
Company contribution	0	0
Actual benefits paid	(57)	(52)
Plan assets at fair value at end of period	1,588	1,559	1,446
Funded status	757	659
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	867	856
Service cost	11	11	17
Interest cost	41	42	27
Plan amendments	(24)	0
Actuarial loss (gain)	(38)	10
Benefits paid	(56)	(52)
Benefit obligation at end of period	801	867	856
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,453	1,350
Actual return on plan assets	80	154
Company contribution	0	0
Actual benefits paid	(54)	(51)
Plan assets at fair value at end of period	1,479	1,453	$ 1,350
Funded status	$ 678	$ 586