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		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 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) included in earnings	[1]	1	(1)
Total gains (losses) offset through regulatory accounting		(2)	2	(15)
Purchases		2	1	(1)
Settlements		(1)	(2)	13
Balance at end of period		1	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	1	4
Total gains (losses) included in earnings	[1]	1
Total gains (losses) offset through regulatory accounting		(2)	2	(15)
Purchases		2		(1)
Settlements		(1)	(2)	13
Balance at end of period		$ 1	$ 1	$ 1

[1] CMS Energy and Consumers record realized gains and losses for Level 3 recurring fair value measurements in earnings as a component of maintenance and other operating expenses or purchased and interchange power on their consolidated statements of income.