Investments in Non-Consolidated Companies (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Equity Method Investment Summarized Financial Information Income Statement [Abstract]
Net sales	$ 4,475.2	$ 4,938.4	$ 4,061.7
Net (loss) earnings	67.5	97.9	0.5
Mosaics share of equity in net (loss) earnings	18.3	13.3	(5.0)
Equity Method Investment Summarized Financial Information Balance Sheet [Abstract]
Total assets of equity method investees	1,841.4	1,776.0	1,690.6
Total liabilities of equity method investees	1,149.8	1,005.0	1,022.5
Mosaics share of equity in net assets of equity method investees	$ 256.4	$ 282.8	$ 247.2