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, 2013		Dec. 31, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 2		$ (2)		$ (3)
Total gains (losses) included in earnings			3	[1]	2	[1]
Total gains (losses) offset through regulatory accounting	3		6		2
Purchases			1		1
Sales					(4)
Settlements	(1)		(6)
Balance at end of period	4		2		(2)
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period	(1)	[1]	2	[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	2		2		1
Total gains (losses) offset through regulatory accounting	3		6		2
Purchases			1		1
Settlements	(1)		(7)		(2)
Balance at end of period	$ 4		$ 2		$ 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.