Financings and Capitalization (Revolving Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Revolving Credit Facilities March 31, 2016 [Member]
Amount of Facility	$ 550	[1]
Amount Borrowed	25	[1]
Letters of Credit Outstanding	2	[1]
Amount Available	523	[1]
Average borrowings	13
Weighted average interest rate	2.27%
LIBOR plus	2.00%
Revolving Credit Facilities March 31, 2016 [Member] | Consumers Energy Company [Member]
Amount of Facility	500	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	3	[2]
Amount Available	497	[2]
Revolving Credit Facilities April 18, 2017 [Member] | Consumers Energy Company [Member]
Amount of Facility	150	[2]
Amount Borrowed		[2]
Amount Available	150	[2]
Revolving Credit Facilities September 9, 2014 [Member] | Consumers Energy Company [Member]
Amount of Facility	30	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	$ 30	[2]

[1] Obligations under this facility are secured by Consumers common stock. CMS Energy's average borrowings during the six months ended June 30, 2012 totaled $13 million, with a weighted-average annual interest rate of 2.27 percent, representing LIBOR plus 2.00 percent.

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