Retirement Benefits (Schedule of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Consumers Energy Company
Regulatory assets
Total regulatory assets	$ 3,886	$ 3,652
DB Pension Plans and DB SERP
Regulatory assets
Net loss	634	724
Prior service cost (credit)	16	21
Total regulatory assets	650	745
AOCI
Net loss (gain)	65	69
Prior service cost (credit)	1	1
Total amounts recognized in regulatory assets and AOCI	716	815
DB Pension Plans and DB SERP | Consumers Energy Company
Regulatory assets
Net loss	634	724
Prior service cost (credit)	16	21
Total regulatory assets	650	745
AOCI
Net loss (gain)	20	20
Total amounts recognized in regulatory assets and AOCI	670	765
OPEB Plan
Regulatory assets
Net loss	191	251
Prior service cost (credit)	(100)	(140)
Total regulatory assets	91	111
AOCI
Net loss (gain)	(3)	2
Prior service cost (credit)	(2)	(3)
Total amounts recognized in regulatory assets and AOCI	86	110
OPEB Plan | Consumers Energy Company
Regulatory assets
Net loss	191	251
Prior service cost (credit)	(100)	(140)
Total regulatory assets	91	111
AOCI
Net loss (gain)	0	0
Total amounts recognized in regulatory assets and AOCI	$ 91	$ 111