Income Taxes (Reconciliation of Beginning and Ending Uncertain Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance at beginning of period	$ 4	$ 62	$ 65
Reductions for prior year tax positions	(1)	(58)	(6)
Additions for prior year tax positions	1		2
Additions for current year tax positions			1
Balance at end of period	4	4	62
Consumers Energy Company [Member]
Balance at beginning of period	3	57	55
Reductions for prior year tax positions		(54)	(1)
Additions for prior year tax positions	1		2
Additions for current year tax positions			1
Balance at end of period	$ 4	$ 3	$ 57