Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Level 3 Inputs) (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 4	$ 2		$ (2)
Total gains (losses) included in earnings				3
Total gains (losses) offset through regulatory accounting	(15)	3		6
Purchases	(1)			1
Settlements	13	(1)		(6)
Balance at end of period	1	4		2
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period		(1)	[1]	2	[1]
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	4	2		2
Total gains (losses) offset through regulatory accounting	(15)	3		6
Purchases	(1)			1
Settlements	13	(1)		(7)
Balance at end of period	$ 1	$ 4		$ 2

[1] CMS Energy records realized and unrealized gains and losses for Level 3 recurring fair value measurements in earnings as a component of operating revenue or maintenance and other operating expenses on its consolidated statements of income.