Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 100	$ 53
Restricted cash equivalents	14	14
Nonqualified deferred compensation plan assets	6	5
Commodity contracts	9	3
Total	266	203
Nonqualified deferred compensation plan liabilities	6	5
Commodity contracts	2	4
Total	8	9
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	84
Restricted cash equivalents	13	13
Nonqualified deferred compensation plan assets	4	4
Commodity contracts	6	2
Total	232	137
Nonqualified deferred compensation plan liabilities	4	4
Total	4	4
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	100	53
Restricted cash equivalents	14	14
Nonqualified deferred compensation plan assets	6	5
Total	257	200
Nonqualified deferred compensation plan liabilities	6	5
Total	6	5
Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	84
Restricted cash equivalents	13	13
Nonqualified deferred compensation plan assets	4	4
Total	226	135
Nonqualified deferred compensation plan liabilities	4	4
Total	4	4
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts	2
Total	2
Commodity contracts	1	3
Total	1	3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts	7	3
Total	7	3
Commodity contracts	1	1
Total	1	1
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts	6	2
Total	6	2
Supplemental Executive Retirement Plan [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value		2
Supplemental Executive Retirement Plan [Member] | Cash Equivalents [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value		1
Supplemental Executive Retirement Plan [Member] | Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	137	126
Supplemental Executive Retirement Plan [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	96	85
Supplemental Executive Retirement Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value		2
Supplemental Executive Retirement Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value		1
Supplemental Executive Retirement Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	137	126
Supplemental Executive Retirement Plan [Member] | Fair Value, Inputs, Level 1 [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	96	85
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	29	32
CMS Energy Common Stock [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	$ 29	$ 32