Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 19	$ 14	$ 5
Additions for current-year tax positions	1	1	10
Additions for prior-year tax positions	3	4	0
Reductions for prior-year tax positions	0	0	(1)
Balance at end of period	23	19	14
Consumers Energy Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	28	21	5
Additions for current-year tax positions	1	2	17
Additions for prior-year tax positions	5	5	0
Reductions for prior-year tax positions	0	0	(1)
Balance at end of period	$ 34	$ 28	$ 21