Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	$ 52	$ 110
Restricted cash equivalents	[1]	52	38
Nonqualified deferred compensation plan assets	[1]	9	8
Commodity contracts	[1]	3	2
Total	[1]	264	289
Nonqualified deferred compensation plan liabilities	[1]	9	8
Commodity contracts	[1]	1	1
Total	[1]	10	9
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]		19
Restricted cash equivalents	[1]	52	38
Nonqualified deferred compensation plan assets	[1]	6	6
Commodity contracts	[1]	2	2
Total	[1]	194	196
Nonqualified deferred compensation plan liabilities	[1]	6	6
Commodity contracts	[1]	1	1
Total	[1]	7	7
DB SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	1	4
DB SERP [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	1	3
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]	147	127
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]	105	90
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]	$ 28	$ 38

[1] All assets and liabilities were classified as Level 1 with the exception of some commodity contracts, which were classified as Level 2 or Level 3 and which were insignificant at September 30, 2015 and December 31, 2014.