Financings and Capitalization (Revolving Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Average borrowings	$ 11
Weighted average interest rate	2.22%
LIBOR plus	2.00%
Revolving Credit Facilities March 31, 2016 [Member]
Amount of Facility	550	[1]
Amount Borrowed		[1]
Letters of Credit Outstanding	3	[1]
Amount Available	547	[1]
Revolving Credit Facilities March 31, 2016 [Member] | Consumers Energy Company [Member]
Amount of Facility	500	[2],[3]
Amount Borrowed		[2],[3]
Letters of Credit Outstanding	1	[2],[3]
Amount Available	499	[2],[3]
Revolving Credit Facilities August 9, 2013 [Member] | Consumers Energy Company [Member]
Amount of Facility	150	[2]
Amount Borrowed		[2]
Amount Available	150	[2]
Revolving Credit Facilities September 21, 2011 [Member] | Consumers Energy Company [Member]
Amount of Facility	30	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	$ 30	[2]

[1] On March 31, 2011, CMS Energy entered into a $550 million secured revolving credit facility with a consortium of banks. This facility has a five-year term and replaced CMS Energy's revolving credit facility that was set to expire in 2012. Obligations under this facility are secured by Consumers common stock. CMS Energy's average borrowings during the year ended December 31, 2011 totaled $11 million, with a weighted-average annual interest rate of 2.22 percent, representing LIBOR 2.00 percent.

[2] Obligations under this facility are secured by FMBs of Consumers.

[3] On March 31, 2011, Consumers entered into a $500 million secured revolving credit facility with a consortium of banks. This facility has a five-year term and replaced Consumers' revolving credit facility that was set to expire in 2012.