Financings And Capitalization (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended			9 Months Ended
		Oct. 25, 2018	Aug. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Jul. 31, 2018
Financing And Capitalization [Line Items]
Principal balance					$ 1,000
Debt retirement, principal					643
Unrestricted retained earnings					4,700
Common stock dividends from Consumers					392
Stock offering program maximum value			$ 250	$ 100
Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance					550
Debt retirement, principal					318
Unrestricted retained earnings					1,300
Consumers Energy Company | Commercial Paper
Financing And Capitalization [Line Items]
Short-term debt, authorized borrowings					500
Short-term debt					279
October 2018 First Mortgage Bonds | Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance						$ 500
Subsequent Event | 3.68% First Mortgage Bonds Due 2027 | Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance		$ 100
Interest Rate		3.68%
Subsequent Event | 4.01% First Mortgage Bonds Due 2038 | Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance		$ 215
Interest Rate		4.01%
Subsequent Event | 4.28% First Mortgage Bonds Due 2057 | Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance		$ 185
Interest Rate		4.28%
CMS Energy Corporation
Financing And Capitalization [Line Items]
Principal balance	[1]				450
Debt retirement, principal					$ 325
CMS Energy Corporation | Subsequent Event | 5.875% Junior Subordinated Notes Due 2078
Financing And Capitalization [Line Items]
Principal balance		$ 30
Interest Rate	[1]	5.875%
CMS Energy Corporation | Subsequent Event | 6.25% Senior Notes Due 2020
Financing And Capitalization [Line Items]
Interest Rate	[1]	6.25%
Loss on extinguishment of debt		$ 11
Debt retirement, principal		$ 300

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