Financings And Capitalization (Major Long-Term Debt Transactions) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)		Sep. 30, 2018 USD ($)
Debt Instrument [Line Items]
Principal balance	$ 1,000		$ 1,000
Debt retirement, principal			643
Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	550		550
Debt retirement, principal			318
First mortgage bonds | Consumers Energy Company
Debt Instrument [Line Items]
Principal balance	$ 550		$ 550
Interest Rate	4.05%		4.05%
Debt issuance date			May 2018
Maturity Date			2048-05
Tax-exempt pollution control revenue bonds | Consumers Energy Company
Debt Instrument [Line Items]
Debt retirement, principal			$ 68
Maturity Date			2018-04
Debt retirement date			April 2018
First mortgage bonds | Consumers Energy Company
Debt Instrument [Line Items]
Debt retirement, principal			$ 250
Interest Rate	5.65%		5.65%
Maturity Date			2018-09
Debt retirement date			May 2018
CMS Energy Corporation
Debt Instrument [Line Items]
Principal balance	$ 450	[1]	$ 450	[1]
Debt retirement, principal			325
CMS Energy Corporation | Junior subordinated notes 5.625% due March 2078
Debt Instrument [Line Items]
Principal balance	$ 200	[1]	$ 200	[1]
Interest Rate	5.625%	[1]	5.625%	[1]
Debt issuance date			March 2018	[1]
Maturity Date	2078-03	[1]	2078-03	[1]
CMS Energy Corporation | Junior subordinated notes 5.875% due October 2078
Debt Instrument [Line Items]
Principal balance	$ 250	[1]	$ 250	[1]
Interest Rate	5.875%	[1]	5.875%	[1]
Debt issuance date			September 2018	[1]
Maturity Date			2078-10	[1]
CMS Energy Corporation | Term loan facility due December 2018
Debt Instrument [Line Items]
Debt retirement, principal			$ 180
Maturity Date	2018-12		2018-12
Debt retirement date			March 2018
CMS Energy Corporation | Term loan facility due August 2018
Debt Instrument [Line Items]
Debt retirement, principal			$ 45
Maturity Date			2018-12
Debt retirement date			August 2018
CMS Energy Corporation | Senior notes 8.75% due June 2019
Debt Instrument [Line Items]
Debt retirement, principal			$ 100	[2]
Interest Rate	8.75%	[2]	8.75%	[2]
Maturity Date			2019-06	[2]
Debt retirement date			June 2018	[2]
Loss on extinguishment of debt			$ 5

[1] These unsecured obligations rank subordinate and junior in right of payment to all of CMS Energy’s existing and future senior indebtedness.

[2] CMS Energy retired these senior notes at a premium and recorded a loss on extinguishment of $5 million in other expense on its consolidated statements of income.