Financings And Capitalization (Revolving Credit Facilities) (Details) $ in Millions	Sep. 30, 2018 USD ($)
Revolving Credit Facilities June 5, 2023 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	$ 850	[1],[2]
Amount Borrowed	0	[1],[2]
Letters of Credit Outstanding	7	[1],[2]
Amount Available	843	[1],[2]
Revolving Credit Facilities November 23, 2019 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	250	[3]
Amount Borrowed	0	[3]
Letters of Credit Outstanding	25	[3]
Amount Available	225	[3]
Revolving Credit Facilities September 9, 2019 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	30	[3]
Amount Borrowed	0	[3]
Letters of Credit Outstanding	30	[3]
Amount Available	0	[3]
CMS Energy Corporation | Revolving Credit Facilities June 5, 2023
Line of Credit Facility [Line Items]
Amount of Facility	550	[4]
Amount Borrowed	0	[4]
Letters of Credit Outstanding	9	[4]
Amount Available	$ 541	[4]

[1] In June 2018, Consumers amended this revolving credit facility by increasing its borrowing capacity to $850 million and extending the expiration date to June 2023.

[2] Obligations under this facility are secured by first mortgage bonds of Consumers.

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

[4] In June 2018, CMS Energy amended this revolving credit facility, eliminating the security provided by Consumers common stock, and extending the expiration date to June 2023.