Financings and Capitalization (Narrative) (Details) - USD ($)		3 Months Ended	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing And Capitalization [Line Items]
Amount available for dividend payments	$ 4,900,000,000	$ 4,900,000,000
Common stock dividends from Consumers		$ 172,000,000
Stock offering program maximum value			$ 250,000,000
Settlement required (in shares)	424,770	424,770
Consumers Energy Company
Financing And Capitalization [Line Items]
Unrestricted retained earnings	$ 1,300,000,000	$ 1,300,000,000
Consumers Energy Company | Commercial Paper
Financing And Capitalization [Line Items]
Short-term debt, authorized borrowings		500,000,000
Short-term debt	30,000,000	$ 30,000,000
Forward Contracts
Financing And Capitalization [Line Items]
Forward sales contracts aggregate price	$ 250,000,000