Income Taxes (Summary of Significant Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current income taxes
Federal	$ 5	$ 6	$ (1)
State and local	1	0	1
Total current income tax expense	6	6	0
Deferred income taxes
Federal	107	4	49
State and local	38	65	49
Total deferred income tax expense	145	69	98
Deferred income tax credit	(4)	18	(3)
Income tax expense	147	93	95
Consumers Energy Company
Current income taxes
Federal	3	(2)	(13)
State and local	2	8	15
Total current income tax expense	5	6	2
Deferred income taxes
Federal	117	50	103
State and local	43	66	54
Total deferred income tax expense	160	116	157
Deferred income tax credit	(4)	18	(3)
Income tax expense	$ 161	$ 140	$ 156