Financings (Revolving Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Mar. 31, 2011	Jun. 30, 2011
Line of Credit Facility, Initiation Date	March 31, 2011
Average borrowings		$ 11
Weighted average interest rate		2.22%
Consumers Energy Company [Member] | Revolving Credit Facilities March 31, 2016 [Member]
Amount of Facility		500	[1],[2]
Amount Borrowed			[1],[2]
Letters of Credit Outstanding		189	[1],[2]
Amount Available		311	[1],[2]
Revolving Credit Facilities March 31, 2016 [Member]
Amount of Facility		550	[3]
Amount Borrowed			[3]
Letters of Credit Outstanding		3	[3]
Amount Available		547	[3]
Consumers Energy Company [Member] | Revolving Credit Facilities August 9, 2013 [Member]
Amount of Facility		150	[1]
Amount Borrowed			[1]
Amount Available		150	[1]
Consumers Energy Company [Member] | Revolving Credit Facilities September 21, 2011 [Member]
Amount of Facility		30	[4]
Amount Borrowed			[4]
Letters of Credit Outstanding		$ 30	[4]
Consumers Energy Company [Member]
Line of Credit Facility, Initiation Date	March 31, 2011

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

[2] 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 replaces Consumers' revolving credit facility that was set to expire in 2012.

[3] 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 replaces 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 six months ended June 30, 2011 totaled $11 million, with a weighted-average annual interest rate of 2.22 percent, representing LIBOR plus 2.00 percent.

[4] Secured revolving letter of credit facility.