Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net (loss) earnings attributable to Mosaic	$ (203.0)	$ 130.8
Basic weighted average number of shares outstanding	378.8	385.5
Dilutive impact of share-based awards	0.0	1.9
Diluted weighted average number of shares outstanding	378.8	387.4
Basic net (loss) earnings per share attributable to Mosaic	$ (0.54)	$ 0.34
Diluted net (loss) earnings per share attributable to Mosaic	$ (0.54)	$ 0.34
Shares subject to issuance upon exercise of stock options excluded from the calculation of diluted earnings per share	2.5	1.6