Retirement Benefits (Schedule of Funded Status of Retirement Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
DB Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$ 2,169	$ 3,070
Service cost	29	41
Interest cost	106	81
Plan amendments	0	0
Actuarial loss (gain)	52	(811)
Benefits paid	(161)	(212)
Benefit obligation at end of period	2,195	2,169	$ 3,070
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	2,820	3,599
Actual return on plan assets	345	(567)
Company contribution	0	0
Actual benefits paid	(161)	(212)
Plan assets at fair value at end of period	3,004	2,820	3,599
Funded status	809	651
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan, Roll Forwards [Abstract]
Funded status	781	632
DB SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	117	149
Service cost	0	0
Interest cost	6	3
Plan amendments	0	0
Actuarial loss (gain)	1	(25)
Benefits paid	(10)	(10)
Benefit obligation at end of period	114	117	149
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	(114)	(117)
DB SERP | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	85	109
Service cost	0	0
Interest cost	4	2
Plan amendments	0	0
Actuarial loss (gain)	1	(19)
Benefits paid	(7)	(7)
Benefit obligation at end of period	83	85	109
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	(83)	(85)
OPEB Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	889	1,166
Service cost	12	17	18
Interest cost	44	28	23
Plan amendments	0	0
Actuarial loss (gain)	9	(274)
Benefits paid	(54)	(48)
Benefit obligation at end of period	900	889	1,166
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,446	1,787
Actual return on plan assets	165	(294)
Company contribution	0	0
Actual benefits paid	(52)	(47)
Plan assets at fair value at end of period	1,559	1,446	1,787
Funded status	659	557
OPEB Plan | Consumers Energy Company
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	856	1,122
Service cost	11	17	17
Interest cost	42	27	23
Plan amendments	0	0
Actuarial loss (gain)	10	(265)
Benefits paid	(52)	(45)
Benefit obligation at end of period	867	856	1,122
Defined Benefit Plan, Roll Forwards [Abstract]
Plan assets at fair value at beginning of period	1,350	1,668
Actual return on plan assets	154	(273)
Company contribution	0	0
Actual benefits paid	(51)	(45)
Plan assets at fair value at end of period	1,453	1,350	$ 1,668
Funded status	$ 586	$ 494