Income Taxes (Significant Components of Income Tax Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Federal	$ 2	$ (21)	$ (12)
State and Local	24	26	17
Total Current Income Tax Expense	26	5	5
Federal, deferred income taxes	207	210	86
State and Local, deferred income taxes	11	13	28
Total Deferred Income Tax Expense	169	223	114
Deferred ITC, net	(4)	(4)	(4)
Tax Expense	191	224	115
CMS Energy Corporation [Member]
Tax Expense	(61)	(50)	(57)
Consumers Energy Company [Member]
Federal	74	(17)	72
State and Local	32	25	24
Total Current Income Tax Expense	106	8	96
Federal, deferred income taxes	159	236	66
State and Local, deferred income taxes	6	14	5
Total Deferred Income Tax Expense	165	250	71
Deferred ITC, net	(4)	(4)	(4)
Tax Expense	267	254	163
State Jurisdiction [Member]
State and Local	$ (49)