Financings And Capitalization (Revolving Credit Facilities) (Details)	3 Months Ended
	Jun. 30, 2018 USD ($)
Revolving Credit Facilities June 5, 2023 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	$ 850,000,000	[1],[2]
Amount Borrowed	0	[1],[2]
Letters of Credit Outstanding	7,000,000	[1],[2]
Amount Available	843,000,000	[1],[2]
Revolving Credit Facilities November 23, 2019 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	250,000,000	[3]
Amount Borrowed	0	[3]
Letters of Credit Outstanding	25,000,000	[3]
Amount Available	225,000,000	[3]
Revolving Credit Facilities September 9, 2019 | Consumers Energy Company
Line of Credit Facility [Line Items]
Amount of Facility	30,000,000	[3]
Amount Borrowed	0	[3]
Letters of Credit Outstanding	30,000,000	[3]
Amount Available	0	[3]
CMS Energy Corporation | Revolving Credit Facilities June 5, 2023
Line of Credit Facility [Line Items]
Amount of Facility	550,000,000	[4]
Amount Borrowed	0	[4]
Letters of Credit Outstanding	1,000,000	[4]
Amount Available	549,000,000	[4]
Average borrowings	$ 23,000,000
Weighted average interest rate	2.81%

[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] During the six months ended June 30, 2018, CMS Energy’s average borrowings totaled $23 million with a weighted-average interest rate of 2.81 percent. 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.