Financings and Capitalization (Major Long-Term Debt Transactions) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)
Debt Instrument [Line Items]
Principal balance	$ 2,334
Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	1,534
First Mortgage Bonds Due August 2051 | Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	$ 575
Interest Rate	3.50%
First Mortgage Bonds Due May 2060 | Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	$ 525
Interest Rate	2.50%
First Mortgage Bonds Due May 2070 | Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	$ 134
Effective interest rate	0.077%
CMS Energy Corporation
Debt Instrument [Line Items]
Principal balance	$ 800
CMS Energy Corporation | Junior subordinated notes
Debt Instrument [Line Items]
Principal balance	$ 500
Interest Rate	4.75%
Debt instrument interest rate reset term	5 years
London Interbank Offered Rate (LIBOR) | First Mortgage Bonds Due May 2070 | Consumers Energy Company
Debt Instrument [Line Items]
Basis spread on variable rate	0.30%
Five-year Treasury Rate | CMS Energy Corporation | Junior subordinated notes
Debt Instrument [Line Items]
Basis spread on variable rate	4.116%
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	0.556%
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%