Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Level 3 Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 1		$ 1	$ 4
Total gains (losses) offset through regulatory accounting	2	$ 1	3	(18)
Purchases				(1)
Settlements			(1)	16
Balance at end of period	3	1	3	1
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period	0	0	0	0
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	1		1	4
Total gains (losses) offset through regulatory accounting	2	1	3	(18)
Purchases				(1)
Settlements			(1)	16
Balance at end of period	$ 3	$ 1	$ 3	$ 1