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Financings and Capitalization (Major Long-Term Debt Transactions) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2020
USD ($)
Debt Instrument [Line Items]  
Principal balance $ 1,175
Consumers Energy Company  
Debt Instrument [Line Items]  
Principal balance 875
First Mortgage Bonds Due August 2051 | Consumers Energy Company  
Debt Instrument [Line Items]  
Principal balance $ 575
Interest Rate 3.50%
CMS Energy Corporation  
Debt Instrument [Line Items]  
Principal balance $ 300
Term Loan Facility Due February 2021 | CMS Energy Corporation | Term loan facility  
Debt Instrument [Line Items]  
Principal balance $ 300
Effective interest rate 1.572%
Term Loan Facility Due February 2021 | London Interbank Offered Rate (LIBOR) | CMS Energy Corporation | Term loan facility  
Debt Instrument [Line Items]  
Basis spread on variable rate 0.50%
Term loan facility due January 2021 | Term loan facility | Consumers Energy Company  
Debt Instrument [Line Items]  
Principal balance $ 300
Effective interest rate 1.466%
Term loan facility due January 2021 | London Interbank Offered Rate (LIBOR) | Term loan facility  
Debt Instrument [Line Items]  
Basis spread on variable rate 0.45%