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Financings and Capitalization (Narrative) (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended 24 Months Ended
Mar. 31, 2020
Apr. 27, 2020
Mar. 31, 2020
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Financing And Capitalization [Line Items]              
Amount available for dividend payments $ 5,200,000,000   $ 5,200,000,000 $ 5,200,000,000      
Common stock dividends from Consumers       219,000,000      
Stock offering program maximum value           $ 250,000,000  
Proceeds from settlement of forward contracts       $ 101,000,000 $ 3,000,000    
Settlement required (in shares) 379,776   379,776 379,776      
Consumers Energy Company              
Financing And Capitalization [Line Items]              
Unrestricted retained earnings $ 1,500,000,000   $ 1,500,000,000 $ 1,500,000,000      
Consumers Energy Company | Commercial Paper              
Financing And Capitalization [Line Items]              
Short-term debt, authorized borrowings       500,000,000      
Short-term debt 0   $ 0 $ 0      
Forward Contracts              
Financing And Capitalization [Line Items]              
Forward sales contracts aggregate price $ 150,000,000           $ 250,000,000
Settlement of Forward Contracts              
Financing And Capitalization [Line Items]              
Settlement of forward contract issued (in shares)     2,017,783        
Forward contract settlement (in dollars per share)     $ 47.95        
Proceeds from settlement of forward contracts     $ 97,000,000        
First Mortgage Bonds due October 2020 | Subsequent Event | Consumers Energy Company              
Financing And Capitalization [Line Items]              
Interest Rate   3.77%          
First Mortgage Bonds | First Mortgage Bonds due October 2020 | Subsequent Event | Consumers Energy Company              
Financing And Capitalization [Line Items]              
Redemption of debt   $ 100,000,000