Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 110	[1]	$ 87
Restricted cash equivalents	38	[1]	16
Nonqualified deferred compensation plan assets	8	[1]	6
Commodity contracts	2	[1]	5
Total	289	[1]	250
Nonqualified deferred compensation plan liabilities	8	[1]	6
Commodity contracts	1	[1]	1
Total	9	[1]	7
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	19	[1]
Restricted cash equivalents	38	[1]	15
Nonqualified deferred compensation plan assets	6	[1]	4
Commodity contracts	2	[1]	4
Total	196	[1]	147
Nonqualified deferred compensation plan liabilities	6	[1]	4
Commodity contracts	1	[1]
Total	7	[1]	4
DB SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4	[1]
DB SERP [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3	[1]
DB SERP [Member] | Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	127	[1]	136
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	90	[1]	95
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	$ 38	[1]	$ 29

[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 December 31, 2014 and 2013.