Financings And Capitalization (Revolving Credit Facilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019
Revolving Credit Facilities June 5, 2023 | Consumers Energy Company
Line of Credit Facility [Line Items]
Expiration Date	Jun. 05, 2023
Amount of Facility	$ 850
Amount Borrowed	15
Letters of Credit Outstanding	7
Amount Available	$ 828
Revolving Credit Facilities September 30, 2025
Line of Credit Facility [Line Items]
Expiration Date	Sep. 30, 2025
Amount of Facility	$ 18
Amount Borrowed	0
Letters of Credit Outstanding	8
Amount Available	$ 10
Revolving Credit Facilities November 19, 2020 | Consumers Energy Company
Line of Credit Facility [Line Items]
Expiration Date	Nov. 19, 2020
Amount of Facility	$ 250
Amount Borrowed	200
Letters of Credit Outstanding	35
Amount Available	$ 15
Revolving Credit Facilities September 9, 2019 | Consumers Energy Company
Line of Credit Facility [Line Items]
Expiration Date	Sep. 09, 2019
Amount of Facility	$ 30
Amount Borrowed	0
Letters of Credit Outstanding	30
Amount Available	0
Revolving credit agreements | Consumers Energy Company
Line of Credit Facility [Line Items]
Average borrowings	$ 3
Weighted average interest rate	3.505%
CMS Energy | Revolving Credit Facilities June 5, 2023
Line of Credit Facility [Line Items]
Expiration Date	Jun. 05, 2023
Amount of Facility	$ 550
Amount Borrowed	30
Letters of Credit Outstanding	1
Amount Available	519
Average borrowings	$ 15
Weighted average interest rate	2.997%
Letter of Credit | Revolving Credit Facilities September 30, 2025
Line of Credit Facility [Line Items]
Amount Available	$ 8
Subsequent Event | CMS Energy | Revolving Credit Facilities June 5, 2023
Line of Credit Facility [Line Items]
Amount Borrowed		$ 73