Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 394	[1]	$ 87	[1]
Restricted cash equivalents	37	[1]	16	[1]
Nonqualified deferred compensation plan assets	8	[1]	6	[1]
Commodity contracts	4	[1]	5	[1]
Total	576	[1]	250	[1]
Nonqualified deferred compensation plan liabilities	8	[1]	6	[1]
Commodity contracts	2	[1]	1	[1]
Total	10	[1]	7	[1]
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	146	[1]
Restricted cash equivalents	37	[1]	15	[1]
Nonqualified deferred compensation plan assets	5	[1]	4	[1]
Commodity contracts	3	[1]	4	[1]
Total	317	[1]	147	[1]
Nonqualified deferred compensation plan liabilities	5	[1]	4	[1]
Commodity contracts	2	[1]
Total	7	[1]	4	[1]
DB SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2	[1]
DB SERP [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1	[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	131	[1]	136	[1]
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	93	[1]	95	[1]
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	$ 32	[1]	$ 29	[1]

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