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
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at beginning of period	$ 1	$ 4
Total gains (losses) offset through regulatory accounting	1	(19)
Settlements	(1)	15
Balance at end of period	1
Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period	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	4
Total gains (losses) offset through regulatory accounting	1	(19)
Settlements	(1)	15
Balance at end of period	$ 1