Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Balance at beginning of period	$ 6	$ 5	$ 4
Additions for current year tax positions		1	2
Additions for prior year tax positions		1	1
Reductions for prior year tax positions		(1)	(2)
Settlements	(1)
Balance at end of period	5	6	5
Consumers Energy Company [Member]
Balance at beginning of period	6	5	4
Additions for current year tax positions		1	2
Additions for prior year tax positions		1	1
Reductions for prior year tax positions		(1)	(2)
Settlements	(1)
Balance at end of period	$ 5	$ 6	$ 5