Financings And Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Principal Balance	$ 3,161	$ 3,161
Debt retirement, principal		1,325
Loss on extinguishment of debt		16	$ 0	$ 16
Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	1,961	1,961
Debt retirement, principal		1,025
Term loans and revolving credit agreements | Term loan facility due January 2021 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	300	300
Debt retirement, principal		300
First Mortgage Bonds | 3.500% First Mortgage Bonds Due 2051 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 575	$ 575
Interest rate	3.50%	3.50%
First Mortgage Bonds | 2.500% First Mortgage Bonds Due 2060 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 525	$ 525
Interest rate	2.50%	2.50%
First Mortgage Bonds | Variable Rate First Mortgage Bonds Due May 2070 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 134	$ 134
First Mortgage Bonds | Variable Rate First Mortgage Bonds Due October 2070 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	127	127
First Mortgage Bonds | 0.350% First Mortgage Bonds Due 2023 | Consumers Energy Company
Debt Instrument [Line Items]
Principal Balance	$ 300	$ 300
Interest rate	0.35%	0.35%
First Mortgage Bonds | 3.770% Percent First Mortgage Bonds Due 2020 | Consumers Energy Company
Debt Instrument [Line Items]
Interest rate	3.77%	3.77%
Debt retirement, principal		$ 100
First Mortgage Bonds | 5.300% First Mortgage Bonds Due 2022 | Consumers Energy Company
Debt Instrument [Line Items]
Interest rate	5.30%	5.30%
Debt retirement, principal		$ 250
First Mortgage Bonds | 2.850% First Mortgage Bonds Due 2022 | Consumers Energy Company
Debt Instrument [Line Items]
Interest rate	2.85%	2.85%
Debt retirement, principal		$ 375
CMS Energy
Debt Instrument [Line Items]
Principal Balance	$ 1,200	1,200
Debt retirement, principal		300
CMS Energy | Term loans and revolving credit agreements | Term Loan Facility Due February 2021
Debt Instrument [Line Items]
Principal Balance	300	$ 300
Debt retirement, principal	100
Basis spread on variable rate		0.50%
CMS Energy | Junior subordinated notes | 4.750% Junior Subordinated Notes Due 2050
Debt Instrument [Line Items]
Principal Balance	$ 500	$ 500
Interest rate	4.75%	4.75%
Interest rate reset term		5 years
CMS Energy | Junior subordinated notes | 4.750% Junior Subordinated Notes Due 2050 | US Treasury (UST) Interest Rate
Debt Instrument [Line Items]
Basis spread on variable rate		4.116%
CMS Energy | Junior subordinated notes | 3.750% Junior Subordinated Notes Due 2050
Debt Instrument [Line Items]
Principal Balance	$ 400	$ 400
Interest rate	3.75%	3.75%
Interest rate reset term		5 years
CMS Energy | Junior subordinated notes | 3.750% Junior Subordinated Notes Due 2050 | US Treasury (UST) Interest Rate
Debt Instrument [Line Items]
Basis spread on variable rate		2.90%
CMS Energy | Senior notes | 5.050% Senior Notes Due 2022
Debt Instrument [Line Items]
Interest rate	5.05%	5.05%
Debt retirement, principal		$ 300
Loss on extinguishment of debt		$ 16