Schedule II - Valuation and Qualifying Accounts and Reserves (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Allowance for uncollectible accounts [Member]
Balance at Beginning of Period	$ 25		$ 23		$ 26
Charged to Expense	70		53		47
Deductions	60		51		50
Balance at End of Period	35		25		23
Allowance for uncollectible accounts [Member] | Consumers Energy Company [Member]
Balance at Beginning of Period	23	[1]	21	[1]	24	[1]
Charged to Expense	70	[1]	53	[1]	47	[1]
Deductions	60	[1]	51	[1]	50	[1]
Balance at End of Period	33	[1]	23	[1]	21	[1]
Deferred tax valuation allowance [Member]
Balance at Beginning of Period	19		34		32
Charged to Expense	1		1		2
Charge to other Accounts			(15)
Deductions			1
Balance at End of Period	20		19		34
Deferred tax valuation allowance [Member] | Consumers Energy Company [Member]
Balance at Beginning of Period
Charged to Expense	1
Charge to other Accounts
Deductions
Balance at End of Period	1
Allowance for notes receivable [Member]
Balance at Beginning of Period	5	[2]	6	[2]	34	[2]
Charged to Expense	4	[2]	4	[2]	7	[2]
Deductions	4	[2]	5	[2]	35	[2]
Balance at End of Period	$ 5	[2]	$ 5	[2]	$ 6	[2]

[1] Deductions are write-offs of uncollectible accounts, net of recoveries.

[2] 1 Deductions are write-offs of uncollectible accounts, net of recoveries.