Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Income available to common stockholders
Net income	$ 213	$ 241
Average common shares outstanding
Weighted average shares - basic (in shares)	282.8	281.5
Dilutive nonvested stock awards (in shares)	0.6	0.7
Dilutive forward equity sale contracts (in shares)	0.2	0.0
Weighted average shares - diluted (in shares)	283.6	282.2
Net income per average common share available to common stockholders
Basic earnings per average common share (in dollars per share)	$ 0.75	$ 0.86
Diluted earnings per average common share (in dollars per share)	$ 0.75	$ 0.86

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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