Derivative Instruments (Assets and Liabilities Fair Value of Derivative Instruments) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Impact of master netting arrangements less than	$ 1		$ 1
Impact of cash margin deposits on derivative liabilities less than	1		1
Consumers Energy Company [Member] | Other Assets [Member] | Commodity Contracts [Member]
Derivative Assets	2		1
Other Assets [Member] | Commodity Contracts [Member]
Derivative Assets	2	[1]	1	[1]
Consumers Energy Company [Member] | Other Liabilities [Member] | Commodity Contracts [Member]
Derivative Liabilities
Other Liabilities [Member] | Commodity Contracts [Member]
Derivative Liabilities	$ 3	[2]	$ 4	[2]

[1] 1 Assets and liabilities are presented gross and exclude the impact of offsetting derivative assets and liabilities under master netting agreements, which was less than $1 million at September 30, 2011 and December 31, 2010.

[2] 2 Liabilities exclude the impact of offsetting cash margin deposits paid by CMS ERM to other parties, which was less than $1 million at September 30, 2011 and December 31, 2010. CMS Energy presents these liabilities net of these impacts on its consolidated balance sheets.