Financings And Capitalization (Narrative) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Financing And Capitalization [Line Items]
Debt issuance		$ 1,025,000,000
Limitation on payment of stock dividends		4,300,000,000
Common stock dividends from Consumers		$ 499,000,000
Common stock, shares authorized		350,000,000	350,000,000
Par value of Common Stock		$ 0.01
Shares of Preferred Stock authorized		10,000,000
Par value of Preferred Stock		$ 0.01
Aggregate sales price of an equity offering program		$ 100,000,000
Term Loan [Member]
Financing And Capitalization [Line Items]
Debt issuance		$ 180,000,000
Debt instrument, extension term		1 year
CMS Energy [Member]
Financing And Capitalization [Line Items]
Debt issuance		$ 575,000,000
Consumers Energy Company [Member]
Financing And Capitalization [Line Items]
Debt issuance		450,000,000
Maximum allowed short term securities outstanding under FERC Authorization		800,000,000
Maximum allowed long-term securites outstanding under FERC Authorization		1,800,000,000
Long-term securities, remaining availability under FERC Authorization		1,300,000,000
Short-term debt, authorized borrowings		800,000,000
Short-term borrowings outstanding		398,000,000
Unrestricted retained earnings		$ 1,000,000,000
Common stock, shares authorized		125,000,000	125,000,000
Consumers Energy Company [Member] | Commercial Paper [Member]
Financing And Capitalization [Line Items]
Weighted average annual interest rate		1.14%
Short-term debt, authorized borrowings		$ 500,000,000
Short-term borrowings outstanding		398,000,000
Revolving Credit Facilities May 27, 2021 [Member]
Financing And Capitalization [Line Items]
Amount of Facility	[1],[2]	550,000,000
Revolving Credit Facilities May 27, 2021 [Member] | Consumers Energy Company [Member]
Financing And Capitalization [Line Items]
Amount of Facility	[2],[3]	$ 650,000,000

[1] During the year ended December 31, 2016, CMS Energy's average borrowings totaled $3 million with a weighted-average interest rate of 1.68 percent. Obligations under this facility are secured by Consumers common stock.

[2] In May 2016, the expiration date of this revolving credit agreement was extended from 2020 to 2021.

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