Financial Instruments (Summary of the Sales Activity for Investment Securities) (Details) (USD $) In Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011		Sep. 30, 2010
Proceeds from Sales of Available-for-Sale Securities	$ 1	[1]		$ 2	[1]	$ 1	[1]
Gross Realized Losses from Sales of Available-for-Sale Securities Less Than	1		1	1		1
Consumers Energy Company [Member]
Proceeds from Sales of Available-for-Sale Securities	1	[1]		1	[1]
Gross Realized Losses from Sales of Available-for-Sale Securities Less Than	$ 1		$ 1	$ 1		$ 1

[1] 1 All of the proceeds related to sales of investments that were held within the SERP and classified as available for sale. Realized losses on these sales were less than $1 million for both CMS Energy and Consumers during each period.