Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 14	$ 5	$ 6
Additions for current-year tax positions	1	10	0
Additions for prior-year tax positions	4	0	0
Reductions for prior-year tax positions	0	(1)	0
Settlements	0	0	(1)
Balance at end of period	19	14	5
Consumers Energy Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	21	5	6
Additions for current-year tax positions	2	17	0
Additions for prior-year tax positions	5	0	0
Reductions for prior-year tax positions	0	(1)	0
Settlements	0	0	(1)
Balance at end of period	$ 28	$ 21	$ 5