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Financings And Capitalization (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Financing And Capitalization [Line Items]    
Debt issuance $ 1,025,000,000  
Limitation on payment of stock dividends 4,300,000,000  
Common stock dividends from Consumers $ 499,000,000  
Common stock, shares authorized 350,000,000 350,000,000
Par value of Common Stock $ 0.01  
Shares of Preferred Stock authorized 10,000,000  
Par value of Preferred Stock $ 0.01  
Aggregate sales price of an equity offering program $ 100,000,000  
Term Loan [Member]    
Financing And Capitalization [Line Items]    
Debt issuance $ 180,000,000  
Debt instrument, extension term 1 year  
CMS Energy [Member]    
Financing And Capitalization [Line Items]    
Debt issuance $ 575,000,000  
Consumers Energy Company [Member]    
Financing And Capitalization [Line Items]    
Debt issuance 450,000,000  
Maximum allowed short term securities outstanding under FERC Authorization 800,000,000  
Maximum allowed long-term securites outstanding under FERC Authorization 1,800,000,000  
Long-term securities, remaining availability under FERC Authorization 1,300,000,000  
Short-term debt, authorized borrowings 800,000,000  
Short-term borrowings outstanding 398,000,000  
Unrestricted retained earnings $ 1,000,000,000  
Common stock, shares authorized 125,000,000 125,000,000
Consumers Energy Company [Member] | Commercial Paper [Member]    
Financing And Capitalization [Line Items]    
Weighted average annual interest rate 1.14%  
Short-term debt, authorized borrowings $ 500,000,000  
Short-term borrowings outstanding 398,000,000  
Revolving Credit Facilities May 27, 2021 [Member]    
Financing And Capitalization [Line Items]    
Amount of Facility [1],[2] 550,000,000  
Revolving Credit Facilities May 27, 2021 [Member] | Consumers Energy Company [Member]    
Financing And Capitalization [Line Items]    
Amount of Facility [2],[3] $ 650,000,000  
[1] During the year ended December 31, 2016, CMS Energy's average borrowings totaled $3 million with a weighted-average interest rate of 1.68 percent. Obligations under this facility are secured by Consumers common stock.
[2] In May 2016, the expiration date of this revolving credit agreement was extended from 2020 to 2021.
[3] Obligations under this facility are secured by first mortgage bonds of Consumers.