Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 27	$ 74
Restricted cash and cash equivalents	21	17
Nonqualified deferred compensation plan assets	14	14
Cash equivalents	1	5
Derivative instruments	1	1
Total	64	252
Nonqualified deferred compensation plan liabilities	14	14
Derivative instruments	3	1
Total	17	15
Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Restricted cash and cash equivalents	17	17
Nonqualified deferred compensation plan assets	10	10
Cash equivalents	0	4
Derivative instruments	1	1
Total	29	155
Nonqualified deferred compensation plan liabilities	10	10
Derivative instruments	0	0
Total	10	10
DB SERP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1	5
Debt securities	0	141
DB SERP | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	4
Debt securities	0	102
DB SERP | Debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	141
DB SERP | Debt securities | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	102
Common Stock | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
CMS Energy common stock	$ 1	$ 21