Financings And Capitalization (Major Long-Term Debt Transactions) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Principal Balance	$ 2,096
Debt retirement, principal	945
Consumers Energy Company
Debt Instrument [Line Items]
Debt retirement, principal	300
First Mortgage Bonds | 3.750% First Mortgage Bonds Due 2050 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 300
Interest rate	3.75%
First Mortgage Bonds | 3.100% First Mortgage Bonds Due 2050 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 550
Interest rate	3.10%
First Mortgage Bonds | Variable Rate First Mortgage Bonds | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 76
First Mortgage Bonds | 5.650% First Mortgage Bonds Due 2020 | Consumers Energy Company
Debt Instrument [Line Items]
Debt retirement, principal	$ 300
Interest rate	5.65%
Tax Exempt Revenue Bonds | Variable Tax Exempt Revenue Bonds Due 2049 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 75
Interest rate	1.80%
First Mortgage Bonds and Tax Exempt Revenue Bonds | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 1,001
CMS Energy
Debt Instrument [Line Items]
Debt retirement, principal	645
CMS Energy | Term Loan Facility Due 2019
Debt Instrument [Line Items]
Debt retirement, principal	300
CMS Energy | Term Loan Facility Due April 2019
Debt Instrument [Line Items]
Debt retirement, principal	180
CMS Energy | Term loans and revolving credit agreements | Term Loan Facility Due 2019
Debt Instrument [Line Items]
Principal Balance	300
CMS Energy | Term loans and revolving credit agreements | Term Loan Facility Due 2020
Debt Instrument [Line Items]
Principal Balance	165
CMS Energy | Junior subordinated notes¹
Debt Instrument [Line Items]
Principal Balance	1,095
CMS Energy | Junior subordinated notes¹ | 5.875% Junior Subordinated Notes Due 2079
Debt Instrument [Line Items]
Principal Balance	$ 630
Interest rate	5.875%
Term Loan Facility Due June 2020 Tranche One | CMS Energy | Term Loan Facility Due 2020
Debt Instrument [Line Items]
Debt retirement, principal	$ 165