Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 548		$ 87
Restricted cash equivalents	15		16
Nonqualified deferred compensation plan assets	7		6
Commodity contracts	2		5
Total	707		250
Nonqualified deferred compensation plan liabilities	7	[1]	6	[1]
Commodity contracts			1	[1]
Total	7	[1]	7	[1]
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	80
Restricted cash equivalents	15		15
Nonqualified deferred compensation plan assets	5		4
Commodity contracts			4
Total	227		147
Nonqualified deferred compensation plan liabilities	5	[1]	4	[1]
Total	5	[1]	4	[1]
DB SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2
DB SERP [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	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	133		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	94		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	$ 32		$ 29

[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.