Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 23	$ 19	$ 14
Additions for current-year tax positions	1	1	1
Additions for prior-year tax positions	3	3	4
Reductions for prior-year tax positions	(2)	0	0
Balance at end of period	25	23	19
Consumers Energy Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	34	28	21
Additions for current-year tax positions	1	1	2
Additions for prior-year tax positions	4	5	5
Reductions for prior-year tax positions	(8)	0	0
Balance at end of period	$ 31	$ 34	$ 28