Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Balance at beginning of period	$ 5	$ 4	$ 1
Additions for current year tax positions	1	2
Additions for prior year tax positions	1	1	3
Reductions for prior year tax positions	(1)	(2)
Balance at end of period	6	5	4
Consumers Energy Company [Member]
Balance at beginning of period	5	4	1
Additions for current year tax positions	1	2
Additions for prior year tax positions	1	1	3
Reductions for prior year tax positions	(1)	(2)
Balance at end of period	$ 6	$ 5	$ 4