Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Jan. 31, 2013	Sep. 30, 2014	Dec. 31, 2013
Financial Instruments [Line Items]
Portion of long-term debt supported by third-party credit enhancements		$ 103	$ 103
Consumers Energy Company [Member]
Financial Instruments [Line Items]
Portion of long-term debt supported by third-party credit enhancements		103	103
Gain on donation of CMS Energy common stock	$ 4