Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	$ 74	$ 44
Restricted cash equivalents	[1]	17	19
Nonqualified deferred compensation plan assets	[1]	14	12
Commodity contracts	[1]	1	1
Total	[1]	252	220
Nonqualified deferred compensation plan liabilities	[1]	14	12
Commodity contracts	[1]	1
Total	[1]	15	12
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash equivalents	[1]	17	19
Nonqualified deferred compensation plan assets	[1]	10	8
Commodity contracts	[1]	1	1
Total	[1]	155	165
Nonqualified deferred compensation plan liabilities	[1]	10	8
Total	[1]	10	8
DB SERP [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	5	3
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]	4	2
DB SERP [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	[1]	141
DB SERP [Member] | Debt Securities [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale - Fair Value	[1]	102
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]		141
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]		102
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]	$ 21	$ 33

[1] All assets and liabilities were classified as Level 1 with the exception of commodity contracts, which were classified as Level 3.