Financings And Capitalization (Revolving Credit Facilities) (Details) (USD $)
In Millions, unless otherwise specified
 9 Months Ended
Sep. 30, 2012
Revolving Credit Facilities March 31, 2016 [Member]
  
Expiration Date Mar. 31, 2016
Amount of Facility $ 550 [1]
Letters of Credit Outstanding 2 [1]
Amount Available 548 [1]
Average borrowings 16
Weighted average interest rate 2.26%
LIBOR plus 2.00%
Revolving Credit Facilities March 31, 2016 [Member] | Consumers Energy Company [Member]
  
Expiration Date Mar. 31, 2016
Amount of Facility 500 [2]
Letters of Credit Outstanding 2 [2]
Amount Available 498 [2]
Revolving Credit Facilities April 18, 2017 [Member] | Consumers Energy Company [Member]
  
Expiration Date Apr. 18, 2017
Amount of Facility 150 [2]
Amount Available 150 [2]
Revolving Credit Facilities September 9, 2014 [Member] | Consumers Energy Company [Member]
  
Expiration Date Sep. 09, 2014
Amount of Facility 30 [2]
Letters of Credit Outstanding $ 30 [2]
[1] In Millions Letters of Credit Expiration DateAmount of Facility Amount Borrowed Outstanding Amount Available CMS EnergyMarch 31, 20161$ 550$ -$ 2$ 548ConsumersMarch 31, 20162$ 500$ -$ 2$ 498April 18, 20172 150 - - 150September 9, 20142 30 - 30 -Obligations under this facility are secured by Consumers common stock. CMS Energy’s average borrowings during the nine months ended September 30, 2012 were $16 million, with a weighted-average annual interest rate of 2.26 percent, representing LIBOR plus 2.00 percent.
[2] Obligations under this facility are secured by FMBs of Consumers.