Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Balance at beginning of period	$ 4	$ 1	$ 4
Additions for current year tax positions	2
Additions for prior year tax positions	1	3	1
Reductions for prior year tax positions	(2)		(4)
Balance at end of period	5	4	1
Consumers Energy Company [Member]
Balance at beginning of period	4	1	4
Additions for current year tax positions	2
Additions for prior year tax positions	1	3	1
Reductions for prior year tax positions	(2)		(4)
Balance at end of period	$ 5	$ 4	$ 1