Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Level 3 Inputs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013		Sep. 30, 2014	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 1	$ 8		$ 4	$ 2
Total gains (losses) offset through regulatory accounting	2	(2)		(16)	5
Purchases		1		(1)
Settlements	(2)	(1)		14	(1)
Balance at end of period	1	6		1	6
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period		1	[1]
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	1	10		4	2
Total gains (losses) offset through regulatory accounting	2	(2)		(16)	5
Purchases		(1)		(1)
Settlements	(2)	(1)		14	(1)
Balance at end of period	$ 1	$ 6		$ 1	$ 6

[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.