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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 3	$ 1	$ 1	$ 4
Total gains (losses) offset through regulatory accounting		2	3	(16)
Purchases				(1)
Settlements	(1)	(2)	(2)	14
Balance at end of period	2	1	2	1
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period	(1)
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	3	1	1	4
Total gains (losses) offset through regulatory accounting		2	3	(16)
Purchases				(1)
Settlements	(1)	(2)	(2)	14
Balance at end of period	$ 2	$ 1	$ 2	$ 1