Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	$ 158	$ 110
Restricted cash equivalents	[1]	19	38
Nonqualified deferred compensation plan assets	[1]	10	8
Commodity contracts	[1]	1	2
Total	[1]	336	289
Nonqualified deferred compensation plan liabilities	[1],[2]	10	8
Commodity contracts	[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]	19	38
Nonqualified deferred compensation plan assets	[1]	7	6
Commodity contracts	[1]	1	2
Total	[1]	162	196
Nonqualified deferred compensation plan liabilities	[1],[2]	7	6
Commodity contracts	[1]		1
Total	[1]	7	7
DB SERP [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	2	4
DB SERP [Member] | Cash Equivalents [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	2	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]	146	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]	104	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]	$ 29	$ 38

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

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