Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	$ 153	$ 158
Restricted cash equivalents	[1]	28	19
Nonqualified deferred compensation plan assets	[1]	11	10
Commodity contracts	[1]	2	1
Total	[1]	339	336
Nonqualified deferred compensation plan liabilities	[1]	11	10
Commodity contracts	[1]	1
Total	[1]	12	10
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash equivalents	[1]	28	19
Nonqualified deferred compensation plan assets	[1]	8	7
Commodity contracts	[1]	2	1
Total	[1]	176	162
Nonqualified deferred compensation plan liabilities	[1]	8	7
Commodity contracts	[1]	1
Total	[1]	9	7
DB SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	1	2
DB SERP [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	1	2
DB SERP [Member] | Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	[1]	144	146
DB SERP [Member] | Mutual Fund [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	[1]	103	104
CMS Energy Common Stock [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	[1]	$ 34	$ 29

[1] All assets and liabilities were classified as Level 1 with the exception of some commodity contracts, which were classified as Level 3.